Mid/Late game power leveling
So, you have either had some misfortune losing your top soldiers, or you just want to train up replacements for when you do lose them
What are some thoughts/tips on how to take your raw squaddies (rookies too if you need to) and training them up while facing tougher enemies.
I'm in a situation now where I simply keep on losing my supports, which is annoying to say the least. Seems the aliens go out of their way to target them, even when I keep them back, and whenever I move them up for a flank shot, or any shot, the aliens just crit them regardless of cover (that's not a whine about anything, just annoying to me that my damn supports seem to be very unlucky lately...).
So how do you all do it?
Also, is there an info on how exp is gained? Is it really only for kills? Do you get some for just hitting an alien, or just for being on a mission?
I'm afraid that the only way to do this is to let your squaddies make every easy kill they can (like not letting your super sniper colonel taking down a wounded muton, for example) in order to give them XP as much as possible. I don't see any trick to make this easier.
You need a bit of luck to as well.
Make sure to equip them with SCOPEs; the extra +10% from that helps. Holo-targeting Heavies with Suppression can help. Some people stick Light Plasma Rifles on their rookies even after they could equip a full Plasma Rifle; I'm undecided about whether it's worth the loss of damage (it really depends on what you're fighting and how aggressively you're moving your rookies up to flank). Psi-capable squaddies can level pretty quickly by using Mindfray to get finishing kills on aliens in the 0-5HP range. Alternatively, a veteran with the psi gift might use Mindfray to soften up an alien before your rookie takes a shot... even if the rookie misses, aliens who have been mindfrayed just won't hit you through full cover and ghost armor. A veteran gifted soldier might also Mind Control an alien to keep it alive and out of the fight while you mop up it's friends, then pre-position it to give your rookie an easy kill when the MC ends (be cautious, because the MC will end on the alien's turn, meaning it will get the first action). Non-gifted (or not-yet-tested) rookies and squaddies don't need to be protected as carefully as veterans, so if you see a minor gamble that might result in getting a kill feel free to take it. The bulk of it just comes down to letting your new guy take every chance that comes along to get an easy kill and being patient.
Experience is gained for kills and completing missions. You get more experience for completing the mission if none of your squad members died during it. A squad member below Captain/Lieutenant rank (I forget which) gets bonus experience the first time they fight tough late-game aliens (e.g., Muton Elites). Obviously, the OTS can speed up your experience gains.
In classic, i used to take 2 trainees along on missions and have the old timers do the softening or be there for backup kills. If i was training new ones, and the mission was a cake walk, the snipers got benched instead.
scope + LPR was a god send for early trainees, due to the +20 aim bonus but as soon as they could start hitting consistently, they would receive a PR or in case of an assault, alloy cannons.
On impossible, in the very late game i used council missions for the training and easier abduction missions. With ghost armor + PR (or alloy cannon) they could sneak up and crit them in the face for a guaranteed kill even at squaddie levels. The rest of the team was there as backup so that when the 2 leftovers from the pack moved, one would die to overwatch and the last one would be critted in the face again. Using ghost armor + cloak, you can move and see if the firing position is safe or not. If there are more enemies in LOS than you want to handle, just... skip his turn and cloak + reposition during the next turn. Really easy 'free' xp via kills.
It's fairly analogous to techniques for capturing live aliens. Finish off the rest of his crew and suppress him and/or flank him until rookie can actually land the shot. Grenades are sometimes useful for killing blow. As someone else already pointed out, ghost armor is the end-all-be-all equipment for powerleveling soldiers. I myself am one of the LPR/SCOPE advocates.
Really, though, at this stage of tech, I don't think I've ever lost a vet. I feel the game sorely lacks any incentive to fill out your barracks with seasoned troops, which is an incredible disappointment. After several campaigns, I've trained up many a rookie just to have them standing there on the launchpad when it comes time to launch final mission. I've pretty much stopped at this point.
Another thing to consider -- way easier in my opinion -- is to not complete your satellite coverage, then farm the abduction missions for new (and experienced) troops.
let the rookie/squaddies get kills and try to bring all your men home alive [additional bonus]
In order to increase the damage output from LPR, you can also Ghost before taking the shot from the rookie, ensuring a critical hit.
In my games all new recruits get grenades. Ranked units take down the enemy and the rookies grenade the crap outa them to ensure the kill. When you have a pair of rookies, and you get the AI to clump up (say on the petrol station map) a pair of grenades can do the buisness taking out full teams. That plus a rocket or two ensures that most units advance quickly. For snipers its a little different as I tend to run them around with a pistol to start with, just so they can get in the action. A plasma pistol is a good sidearm, and can be just as effective as a regular rifle.
For me to start leveling a new recruit, he must have psi abilities, otherwise it's a waste of time (i suppose that you already have 10-12 high level not-psi troops)
So you don't need another not gifted grunt. Dress him up with a ghost armor (for all the bonus you get) and give him a LPR along with a scope. This way you'll have a mind-freying rookie, with excellent aim, ghosting ability etc...
Always have him make last kill, and always bring home full numbers (you get extra xp)
Hope this helped
Having a squad with one rookie/squaddie makes it relatively easy to rank them up, without impairing the squad's combat abilities. I typically "retire" colonels, and put rookies in their place, only bringing them back out again for the special missions (alien base, temple ship, battleship, overseer) and that helps the mid-late game squad rotate and skill up - whilst not putting any of my maxed out soldiers at risk.
Freeze alien with suppression or overwatch trick (http://youtu.be/4i-bFs2q_KI)
And let your rookie kill them.