I usually go with a theme. For my son, I had a mickey mouse cake cos he was born in the year of the rat and we decided to go for a MM theme with cake, cutlery, decor and goody packs.
For my gal, we had elmo for 1st bday, sesame St for 2nd bday, "Chocolate Chocolate!" for 3rd bday cos she shares the same bday with 2 other very close relatives, Disney Princess for 5th bday, "Beary Loveable" for 6th bday. Have not decided what we will do for her 7th this year yet.
I usually decide on the theme, then look for pictures to custom the cakes. I go to ecreative cos they are more accomodating and the cake is not bad + there's free delivery above a certain cost. For home celebrations, I try as much as possible to DIY the decor. If not, then I'll online shop for the items I want. I usually get those helium foil balloons from party shops for the kids to bring home.
For sch celebrations, I'll do a goody bag in the theme the birthday child chose to give out.