My advice to new guy(s) for keeping soldiers alive:
Rush Laser cannon for profit (If playing with mods, you might want to rush motion scanners to make some cash as unlike vanilla it might take you a little longer to reach laser cannon). Early use Laser Rifles on the battle field and rush heavy plasma for snipers but keep with laser rifle for scouts until they max reaction.
I have mods so it takes little longer for plasma weapons so I rush heavy flash rifle instead.
Large rockets for heavies->heavy launcher->blaster launcher=optimal. Grenadier uses HE. (You might want use Ammo mule in early missions to carry extra rockets/HE)
After generally try to rush personal Armour and then medikits once i have laser cannon. Saved me a lot of soldiers (albeit sickbay is always full). Also make sure you have at least one guy with motion scanner on each mission (remember the bigger the blimp on scanner the less TUs the entity has so pay attention to location as well as size of blimp)
I personally like 14 soldier team to start with' you know very soon you will have 14 universal soldiers instead of 10 or 8 etc. I just think soldiers are more valuable than tanks due to exp. But certainly keep a few tanks lying around for base defense & once you have the bigger transporter (use them as scout & don't necessarily have to use their guns too).
Grenadier + heavies clear buildings by flattening them. Snipers support scouts. Scouts spot aliens (scouts become valuable later on so don't kill them off unnecessarily (albeit the casualty rates of Xcom scouts are among the highest of any of the roles- but every soldier knew what he/she is signing up for).
In my current campaign I already have some of my scouts hitting my cap of 105 reaction ( I am currently in August 1999).
I also aim to equip every soldier with x1 alien grenade x3 smoke grenade x1 medikit (make sure you prime smoke grenade in soldier equip screen while still in your base, that way the game will always remember to auto prime them for you in future). Bare minimum is x1-2 smoke grenades if the soldier is still weakling.
Tactics:
1. Throw Smoke grenade on floor just in front of skyranger ramp, let the aliens have a turn and deploy on turn 2 (make sure you use motion scanner. once available during turn 2 to check if there is any activity around skyranger just prior to deploying on turn 2). If you see any alien out of the skyranger on Turn 1 make sure to
kill it!
(but to avoid reaction fire have the 2nd row guy throw (here you have to throw
NOT drop), a smoke grenade inside the skyranger then shoot away at will).
2. After deploying, position your snipers in optimal spots (move them if needed to find that sweet spot). Sweep battlefield with scouts in a circular direction away from skyranger. If a scout spots alien have the sniper neutralise the alien (since snipers are ideally far in the back row it wont provoke reaction fire).
Ensure the scouts have the backing of at-least one sniper. If you need to move the snipers to better position then do so, but then don't move scouts forward that turn (otherwise all you're doing is throwing in bait without the hook).
If a scout comes across an obstacle/building have the heavy team/grenadier clear the building before proceeding further.
3. Always leave 4 TUs at end of scouts turn to drop primed smoke grenade on floor (don't throw the smoke grenade simply drag from
shoulder inventory to floor, this way you only use 4TUs). SG will explode upon hitting alien turn button providing cover for your scout.
Never rely on reaction fire unless you have full TUs (*formulae for reaction fire is TUs remaining/maximum TUs * Reaction Stat). So as you can see having full TUs is important to react fire (hence why you'll be using smoke grenades to save your scouts and not reaction fire most of the times). Albeit reaction fire will come in handy as the scouts improve this stat (usually once you start hitting 85+), to blockade/suppress fire.
4. Assaulting Ufos/Bases is risky. This is where most of my casualties come from. Never even think about doing this without at least a motion scanners (optimal weaponry and good soldiers is always handy for alien bases).
As per usual use smoke grenades to provide cover. When dealing with UFOs I usually stay outside (the Aliens just love to rush out). If needed I will assault the UFO, but only to neutralise the last of the aliens once the majority have been neutralised outside UFO.
5. Never do night missions period, they will always certainly end in casualties (as your vision is severely reduced while Aliens can see as if it was day time). If you get a night terror mission just keep locked on the terror mission with interceptors +/- skyranger until day time then assault. If absolutely dead set on assaulting at night flares are a must; don't even think about it without them.
EDIT:
My selection criteria for new recruits (the rest get fired on spot):
Grenadier- 35+ strength; 65+ throwing;
Scout- 50+ reaction; 50+ FA;
Heavy- 35+ str 55+ FA;
Sniper 60+ FA
Ammo Mule (whatever as long as str 35+)
hmmm... I probably missed a few things but that's the grit of it.
