I rarely investigate which ones are in specific the filler episodes. And to be honest I don't think that filler means that is bad, some side stories can be quite interesting, changing dynamics or deepening our understanding of the bonds between different characters. So I usually watch them.
There is only one anime that I would probably skip the fillers and that's One Piece, if only so in my first viewing I can get up to speed to where the anime is right now. The filler episodes then could give me something to do while the waiting game for the newest season is taking place.