I've got Robins & Blue-tits... I think

Hi, I'm totally new here, but I'm a nature lover... using this site I now know I have some blue-tits visiting my bird-box, I live in Brighton and near the sea also, next to my balcony I have a large bush (not sure of it's name) but from there the blue-tits and very occasionally a lone Robin comes to inspect my bird-box which is full of seeds etc, I just wondered If i haven't over filled it, it's now half full of expensive seeds from waitrose... doh, so I need some advise to make my little visitors happier, I love filming them also... got an expensive camera just for the job, amazing... I didn't really realize how special birds are, I can see why you like them :) so if you could offer me some advice I'd love to hear it and thank you for a wonderful site, cheers A