Do research in the community. Part of the reason there is a ban section is to discuss how we've been banned recently or in the past.
Read the last few pages of a script's thread before use and see how many people posted about being banned and how long they were running it for/when they were running it.
I used extreme pest control and botted full range void in like 3 days with it. Mind you I did this very recklessly and am very lucky to not have been banned by it.
f2p pure pking is pretty basic. 40 attack however high strength you want and a range level to match that strength level. Watch how you train your stats because hp will set your combat level off and you'll end up fighting people with higher stats than you.
other than that I pk on my main in f2p all the time for shits and giggles because full rune fights rarely end in a k0.