How do you usually balance your main rotor blades  ?
Reason I am asking is that i had the covering on my Raptor 50's blades come off the edge a little bit, so I used some glue to stick that, and put a little bit of epoxy to seal off the open wood. It is just a little bit. However since its the tip of the blade, I am concerned it may cause vibration.

Any ideas on how to balance this ?

Basically put each blade on a pivoted place to find the CG, mark it, and compare the marks to see where you need to put pieces of tape to balance the weight.  It is simpler to use a purpose built blade balancing stand.

I haven't done this much for myself, as I try to get factory balanced blades of trusted brands, and have not been crashing (knicking the blades) all that often recently.  For the type of flying I like/do, I cannot take risks with unknown blade brands or any kind of damaged blades... that would be a fool hardy thing to do.

this link could help you
http://www.helifreak.com/showthread.php?t=41692
download the one about blade balancing and finless shows how to dynamically balance blades... but again as anwar states its not worth it to use any bad blades or crashed blades in a heli. you "could" end up with a crash...