Good show, friendo! Getting that YouTube chock full with vids sounds like an awesome plan. As far as strategies go, it depends on what you're looking into (high rounds, speed runs, safe zones, etc). Still, I think all the strategies that people will come up with can be of much benefit and may even give you new insight on the maps themselves.
Nacht der Untoten
You can do figure 8's around the thin walls of the Mystery Box room. Hug the wall as tightly as possible to allow space in between. If you feel uncomfortable getting too close to the zombies, a little bit of circling can help as well. I would leave the stairs blocked off in that room to allow only one major spawn (initial room) alongside the four other entrances. And if you're playing the Black Ops version, Thundergun will go a long way as a third weapon choice with Mule Kick.
Verruckt
Circling around the entire facility should do you just fine, if you're playing solo of course. Otherwise, you can hold up for a good amount of time in the Speed Cola room with the k!tch3n [i still can't say that word, damn] inaccessible. This creates only one barrier behind the group and the rest to consolidate into two pathways, eventually merging into the hallway (you can keep buying Bouncing Betties to make this flow nicely). The traps also force the zeds to come up the stairs and the back barrier only.
Shi No Numa
The area right after passing the flogger makes great for tight training. In addition, it helps during Hellhound rounds. Not only do you have a trap available right next to you, but there's ton of running space to go around that location so you don't feel cornered. You could also do a bit of running towards the Doctor's hut (I think it is) and run around in the muddy waters...though it will constrict your movement severely.
Der Riese
As if strategies haven't been done to death on this one map. Honestly though, I find training next to the power switch to be superior as a solo strategy. A trap handy with a potential Mystery Box spawn and an MP40 or FG42 nearby? Sounds like a good plan to be - and it hasn't failed me yet. If you have teammates, keep them camped up on the catwalk with perhaps another one doing thinner trains down on the lab floor.
Kino der Toten
Stage stage stage stage stage. It's been tested and proven on solo and co-op. If with teammates, you could also holdout in the supply room (above the theater past the alley) while keeping the stairwell to the theater closed off. Have two people stand ground facing the alley and two defending the barriers inside the room itself. There is also a chance of a Mystery Box spawn and the AK74-u in the alley.
FIVE
Good luck.
Just kidding. You can do a bit of holding out in the MPL hallway before heading out down below into the control room. Either keep things situation on the catwalk, or back yourselves into the large elevator, switching back and forth between the basement elevator and rising back to the control room elevator. The switch acts as a defense mechanism and can allow some time to revive a fallen teammate, set claymores, the works.
Another strategy you can try involves the Pack-a-Punch room. Every round, hold out somewhere until you hit all the switches to reach the final Defcon level. Get into the PaP room, and prepare to hollow out the incoming horde waiting outside. Rinse and repeat. If combined with the elevator trick, this may save time for the Defcon levels to reset after leaving the PaP room.
On a solo run, you can have the entire floor of the control room to yourself. Open up the barriers and enjoy running a severely tight but effective training around the entire room.
Ascension
Too easy, but you could do various training at the lander station near PhD Flopper, the Claymore area/lander station, outside of Pack-a-Punch, in spawn underneath the spinning mechanism, so on and so forth.
Call of the Dead
There are two major training sessions I see with this map: spawn and the AK74-u area. The good thing about these is that there are weapons available in each and a body of water to cool of George in case he's busting your balls. I feel that both are superior and equivalent but I personally enjoy spawn because 1) it's more open 2) more escape routes 3) delay where zombies slow down in water unless they're sprinting 4) Quick Revive machine.
Shangri-la
Much similar to FIVE, but a little more vast in terms of landscape and movement. Solo will call for running around the entire map at some point with the Shrink Ray, and before that, may require a bit of training the AK74-u room before accessing the door to PhD Flopper. If in co-op, you could possibly hold out on the bridge or on the railcart. This is very team-oriented unless you're absolutely godlike in dragging or cutbacks.
Moon
My favorite map of all time. What strategies CAN'T you do here? I personally love heading to the Ak74-u area and just circling around the rock. 9/10 times you won't be hit because the zombies will be too busy floating while you race them around the perimeter. If that's not your style of training, you can go old school by fending off in the Biodome. Co-op makes this a breeze since every person will have their own area to contain and not that many zombies. The only downfall to this is the lack of weapons to constantly access and the perilous event of an oxygen breaching via excavator.
Having someone with Hacker on hand, however, will not only prevent excavators from reaching the Biodome in time but also allows for Max Ammos up the wahzoo.
Tranzit :: Green Run
There is literally no strategy for this map. You can train at the Bus Depot, the tunnels, outside of the garage at the Diner, around the truck in Farm, bouncing between buildings in Town, anything. The safest would be Town, Diner, and the tunnels. It's your pick at that point.
Town offers Juggernog but no weapon access so you may have to teleport or be patient and wait for the bus to roll by with the B23R in it. Diner has the MP5 and Speed Cola nearby, alongside unlimited Zombie Shields. This makes Diner the best of the three, but requires tighter training than the others. Tunnels is more open for running but only has the M16 available (although it works well when PaP'ed into the Skullcrusher).
Nuketown
Backyards are a must. You may be required to do many, many cutbacks because zombies will be hopping over fences and diving through the doorways on the first floor of the houses. In the long run, it's worth it since you're almost guaranteed a Mystery Box spawn every time and a good perk machine near by. If one backyard doesn't have what you like, use the other. Also, Mustang & Sally all the way.
Die Rise
Buddha Room is a great choice for holdout out with teammates or running solo. If you run solo, use the floor as your running space with the balcony access and broken pole to your advantage. If with teammates, have one person run on the floor and three camp up top to block barriers and protect the runner below here and there.
Another place would be the dragon rooftops, right next to the NavCard table. If all teammates huddle there with one Trample Steam behind the group (right into the barrier), you'll be safe for a long time. Create your own "Claymore Garden" underneath the rampway in case you need to kill off a group of zombies and haven't the ammo to do so. Sliquifier is fairly dangerous here. I would advise having an upgraded SVU on hand and possible an An-94. If you're lucky, the Pack-a-Punch and Juggernog machine will be in the neighboring elevators instead of the lonely corner.
Mob of the Dead
It's like a heightened version of Shangri-la and Five, but with a little more space. Most people find the cafeteria to be the perfect training zone, but I honestly call for the Golden Gate Bridge. Rounds go blazing up there and you can leave at anytime you'd like. Of course, the cost of that is having to collect all the fuel again but honestly it isn't that bad if you switch off between the cafeteria during fuel time and the bridge for hitting rounds.
If possible, obtain the Hell's Redeemer asap. An insanely powerful weapon that cuts through multiple zombies, has unlimited ammo, and makes Brutus a cinch to kill. It works wonders in both locations mentioned.
Buried
Not much going on in the training department, but you could technically start a nice-sized cluster if you run around between the general store and original Mystery Box spawn. It's a tight fit but can work given you have a good arsenal on hand.
But that's not your cup of tea, right? Then camping out is ideal for this map. Take a stand in the Juggernog alley, or access the inside of the courthouse via Paralyzer/Trample Steam and leave the front door closed off. I like both to be honest, but I know the latter works tremendously since you're controlling the spawn points, flow, and barriers. With teammates, the courthouse is a MUST.
Origins
Too many technicalities with this map, but you could train in various areas of the muddy wasteland. Generator 4 (Juggernog area) is always accessible for training, with several looping options available. I tend run around the MP40 mudpit and the Wind Tunnel, making my loop bigger than if I included the generator spot. Tighter training can be done in the mudpit of Generator 5 where the soul crate is. The only consequence of running these is having the giant robots step in your path, making the training process more constricted often until they leave the spots.
Professionals will utilize the muddy road outside the tank station (where the tank rolls in). Despite having your movement reduced, it actually works well if you have a staff. I've even seen @Chopper use this area several times when he streamed Origins along many other famous high rounders with only an upgraded Ice Staff (sometimes even not upgraded!). A couple of charged shots, and whoosh - round is over. You will find a Max Ammo before running out of firepower, but very seldom will you actually not get one. A Boomhilda will come in handy nonetheless, and possible Monkey Bombs/Airstrikes to get zombies off your tail. The good thing with this strategy is that you won't ever need to worry about the giant robots, and there's an MP40 within the station if you need ammo (although if you have the staff, you probably won't be needing a secondary rifle).
I know these are fairly vague but they are condensed so you get the basics.