This will be a overall farming guide, being honest, about farming those most you need:
-Unity
-BoS patrol
-NCR Army
For all of these encoutners I recommend using Taxi character on sandboxie + Farmer character - pure fighter, that will minimise the costs of the farm, and maximize the efficiency of it.
Here's an example Taxi build :
It can use P90 or any other gun to take down under minus HP's critters, to not destroy armors and to not waste ammo.
Next, for Unity I recommend using Laserspammer/BG hybrid - why? Because you'll use weapons which you farm, again making costs minimal, and still, making this easy (220 Supermuties, 128 Ghouls, 193 Men and 145 Women - says all)
There is an example build I use:
I mostly use Laser Rifle and Minigun in the other hand for metal armor guys and girls :-).
For NCR Army I've made a special build, and farmed 70 CA mk2 sets cannot be false.
Basically those 3 builds let you farm anything in game, for BoS patrolmen you'll need to use Big gunner farmer build and taxi.
Basic tips:
-Use sandboxie, if you do not have a friend to run with taxi/fighter.
-Search for encounter in which your target will fight another one to minimise costs of fights (stims, ammo).
For Example:
Unity vs Rogues
NCR Army vs Raiders/Maruders
BoS patrol vs Floaters
and so on.
-You can also use natural obstacles to hide behind and shoot from the cover.
-Always remember your main targets:
In Unity patrol Laser Rifle SuperMutant and Rocketmen
In NCR Army M60 and LSW dudes
In BoS patrol Avenger dude.(eventually if you use psycho& beer, then rocketmen).
(Also, it's important, that with these builds you do not need to use drugs, Imho you shouldn't spend cash on drugs to farm something, it's obsolete.)
- Always have radio with your characters, set at the same channel, so if you're out of stims/injured, send a help signal and go out by second character and return when you're ready.
-Do not collect gear you don't need, science it instead.
-Farming at 24 lvl is sadly recommended, because below you'll be easier target for NPCs.
-Do not use plasma rifle to farm NCR Army, you'll melt armors!
-And finally, share loot with your friends, if they're helping you.
Trader tips:
If you got the farmed stuff, keep it, you can sell it for quite big cash, even doing each day 30k caps.
Mostly recomended to take are : laser rifles, explosive rockets, miniguns.
These you can sell in shops for caps each 3 hours, getting a lot of caps.
The basic route of your should be starting from Den, selling rockets and big guns, going to New Reno, selling there big guns also, then to BH, selling big guns also, then NCR, also big guns, then to Hub, there you can sell big guns in Old Town, and laser rifles on Market for caps/drugs, then go to Necropolis, sell your laser rifles there for caps/drugs/ammo, then go to Gun Runners, sell there bgs for ammo/caps, then finally San Fran, in two shops sell your laser rifles, and on Tanker sell your big guns.
That's all from my side, remember, farming is easier and faster than crafting, and it can teach you about tactics in game, and you won't be bored so much. Enjoy!
Edit: Also, you can farm other encounters, such as Hub patrol (They have CA), VC patrol (They have sniper rifles), of Press Gang/Mercenaries (they have small energy weapons and SEC)
Edit2: Important! I didn't add any values about places where do you encounter them, I made this to not get you killed by PKs.