Is there a theoretical area the group is weak on? If this is the case then perhaps you could research this and explain it to the others through internal educational talks or articles. It's generally impossible for everyone to know everything so its a good idea for people to specialise a little providing they also explain what they discover to everyone.
Is there a practical skill (e.g. Desk Top Publishing) the group is lacking that you could learn or already know? Can you teach this to others?
Is there a struggle you can get involved in that no-one else is currently involved in? Perhaps help is needed in particular struggles the group is already involved in. Perhaps you should get involved in a particular area of struggle to confront you own prejudices or just to find out how things function.
You should start slowly, volunteer for simple stuff first and as you understand how things work (and how much you can sustain) take more things on.
These are practical contributions you can make to building the group and really you should be looking for ways to do one of each. A lot of them are things you can do right from the start.