Are there things that I should do, and things that I should avoid doing?
maybe a few... we take off shoes when we enter to someone's house - but it's common that your host will tell you not to do that - and then this is ok to not take them off ;)
For example, when greeting, how many times do you kiss on cheeks? I've heard its a European thing.
It's common by some people... personally I don't understand this - sometimes it's acceptable to kiss on cheek(s) when you meet your familly (female). Still... this is personall thing and depends on you - nobody (except your grand mother maybe?) will expect that.
Also, when do you call someone by 'sir'('pan') or 'ma'am'('pani'). Do you call people around your same age group by 'pan' or 'pani', or do you talk by using 'you' ('ty')?
Again.. depends on situation. When you talk to clerk in shop, postman, policeman, some stranger met on the street (say aged >20yrs) then you will rather use official form (sir - pan). In less official situations it is rather ok to call someone by 'Ty'.
Any pointers on how to behave in Poland?
naturally, this is not an Asia, Africa .... Poland is modern EU country, very similar standards to US ones...