I feel like I'm being taken for granted?

I'm feeling like friends take me for granted and I don't know what I can do to make them take more notice of me. I know a lot of people will say they aren't my friends etc. but I get on really well with them and there's no contempt or anything, just I feel like they forget me and leave me on the outside sometimes... I've always tried to make an effort and I haven't ever argued with any of them, so I don't know why this happens or what I can do to stop it?