My acoustic guitar (It's a Palmer, don't know what model) tunes out really easily. Is there someway I could tighten the pegs? It has those + screws on the middle of each peg that I think keeps them on or something, should I just tighten those? if you don't understand what I mean, I might add pics later.
you can tighten those screws turn the tuner while doing so to make sure you dont overtighten it . also there may be a 6 sided nut on top of the tuner that can be tightened as well on some models remember to not overtighten as well

also try to make sure you are always going down past the note then tuning up to it so you dont have any slack in the gears of the tuning machine

also lubricate the nut slot with graphite or pencil lead and new strings help tuning stability as well. give your self a wrap or two on the post to counter slipping.