I know for me personally, I feel loved when my friends know me well. When they remember things I've said, my likes and dislikes. It's lovely getting a birthday present which is so 'you'.
It's not a great feeling getting given clothes as a gift that are three sizes too big (when they're around me regularly).
On the contrary, it's fantastic getting quirky, useful presents because they know I'm not a fan of clutter and dust collectors.
One way to get ideas on how to bless your friends is to really listen to what they say and save messages where they mention interests, likes/dislikes etc. Carry a notebook and write it down, or make a note in your phone. If you're out shopping and see something they'd like, buy it and save it until their birthday. Those 'getting to know you' questionnaires circulated via email and Facebook are excellent for getting to know your friends better.
Study your friends and look for ways to bless them.