Fallout1/2: Pick Gifted and Fast shot/small Frame/Finesse as traits. The others are pretty much useless. Tag small Guns and Speech, the most useful skills in the Game. You don't need more than 5 ST and 4 EN. INT and AG should never be below 8.
Stick to one Combat Skill in the Beginning. A skill level of 150 is enough to get eye shots from any reasoable range. You can raise Energy Weapons later(Big Weapons are useless in FO1)
Traps is useless, so is Throwing, Barte and Gambling.
First aid, Doctor, Steal, Outdoorsman are good, but don't spend points if you got better skills you can raise.
Science and Repair are useful later, but you can raise those with books, so don't spend points until you have to
Raise Peech and your combat skill to 100 as soon as possible.(raising a skill other than one for combat above 100 is a waste)
Perks that give you skill points or help you gain levels are useless(except Living Anatomy), as well as most other perks that don't help you in combat(though bonus ranged/melee damage are not worth it)
Hit point gain per level is 2+EN/2.
The number of Party members you can get is CH/2 in FO2 (there is no Limit in FO1).
If you raise the difficulty your skill level drops. You can do this temporarily to get more mileage out of books(doesn't work with combat skills).
Install the Restoration Project for Fallout2, it makes the game even better.
Don't use AP ammo if you didn't install a mod to fix them.
Go for the eyes, though crippling legs can send most critters running.(Groin shots are also effective and damn funny ^^).
Grenades are rare an therefore useless(see throwing).
You can raise every stat except AG and EN by at least 1 without perks(+1 memory module for STR, CHR, INT and PE, +4 STR with power armor, mirrored shades[dig up graves in Golgotha] give +1 CHR if you have them in an item slot and the zeta scan in NCR gives you either +2 or -1 LK, so save first.) With the Restoration Project you can raise AG by 1 at the EPA.
Watch out if you give your party members burst weapons, because they can do a lot of damage to your enemy, as well as yourself.(Ian is infamous for being more dangerous to the player than the enemies)
W40K Cahosgate: The difficulty of the later missions depends on how many marines survived the earlier ones, since high level marines are way more effective.
Use all heavy weapon slots in your Teams.
Flamers are pretty useless, except against a big group of cultists or something.
Power Weapons are good versus armor.
Plasma ammo is rare, so save it for demons, chaos sorcerors and the like.
Don't fight in close combat, unless you are sure can win.(Fighting Demons other than Horrors in close combat is suicide, chaos marines can be tough, but if you shoot at them with a Bolter for a few times first, they go down easy. Cultists are cannon fodder. Melee against vehicles is effective with power weapons, but watch out and don't make a habit of it.)
Melta Bombs have a big range, so watch out!
Do the side missions and kill every enemy on every map, you need the xp.
Jagged Alliance 2:
Get the v1.13 mod, it makes the game a lot more fun.(and more complicated, so if you didn't play it before you may want to play vanilla for a bit first.)
Pump up Wisdom and Health as far as you can, since they hardly rise during the game. Explosives, Medicine, and Tech is pretty pointless. Your mercs can do that a lot better than your AE.
Fighting at night makes everything easier, especially with mercs who have traits for that kind of thing.
Hire cheap mercs with high wisdom, it's cheaper in the long run and they just as good as high level mercs later in the game.
Equipment for every merc should include: A gun with about 3-5 mags, a first aid kit, a knife, gas mask, NV goggles, sun goggles, a water flask, a med kit for your doc and a lock pick and tool kit for your tech expert. Later you should include a heavy weapon expert with heavy weapons(mortars are awesome!).
Mortars can kill a group of enemies from across the map, so if you can get one, get it and get as much ammo as you can.
When you have conquered the airport in drassen or meduna, you can use bobby rays.
Don't recruit Devin, since he is a good source of explosives(if you can find him. He changes bars every couple of days).
If the enemy didn't notice you, you can often get an instant kill with a throwing knife.(if it doesn't work at first, try quickloading.)
For v1.13 only:
Tracer ammo works both ways, so watch out.
Glaser is basically HP ammo that more useful against unarmored, and more useless against armored targets.
A silencer alone won't cut it, you need cold ammo to be really stealthy.
Use Automatic weapons for suppression fire(a new feature in v1.13).
Moltov cocktails/Mustard gas grenades are extremly effective at blocking an entrance and can do a lot of damage if the enemy stays in the fire for more than one round. A combination of supression fire/vacuum grenades/tear gas and Molotov cocktails/mustard gas works wonders against a big group of enemies.
By stuffing things in a backpack and putting that in another backpack you can carry a crapload of stuff at once. Use this if you want carry a lot of stuff from one sector to another. Weight is still accounted for, so it will take a while. This is obviously not a good strategy in a fight, so just use it for shifting things around.
Whew. TL;DR I guess, but whatever I had fun writing it.
Maybe I'll post some more later