Craft some greasu gun and a lot of ammo. Find encounter centaurs vs floaters/allients/fire gecko/death claws. Wait until they will fight with each other. If any of them are going towards you just hit them once with signle shot and they'll change they aim.
Then burst one by one from one hex. Do like this until you reach 15 lvl and will be able to pick Silent Death perk.
After that you should have like +200 to sneak skill, so you are keep searching for the same encounters, but with active sneak skill. Wait until they will fight against each other and then kill one by one standing behind them and beeing in the sneak mode. Auto critt guaranted. if you will have better critt perk (which is simply essential perk for sneaker) it should take maximum 3 shoots per critter to kill.
But remember that after your attack the sneak mode disapear so you'll need to active this mode once again before shooting. If you will pick this strategy it's better to use a gun like magnum/14mm pistol or .223 pistol as these have the best dmg ingame, which make your critical attacks more deadly and effective.
Or simply keep staying with the bursting mode, since 0,45 is easy to craft as hell.