Members. You ideally want to have enough permanent members to keep the faction afloat, but you also want enough to do the work your faction will be doing.
Assets. You need credits, to build cities to make more credits, buy what your faction needs, and pay your members.
Ships. They are usually the most important asset a faction can have, because while they can give you capitol, they are also how you're going to move members, vehicles, items, rms, etc. They're the heart's blood of any real faction.
Determination. If you're not willing to push hard, don't bother.
I'm sure others will give you more detailed information and such, but that should give you an idea, the rest is really up to you and the members of said faction.(Or soon to be faction.)
Interested in coming to my funeral? Talk to Mike Que-kara about getting on the guest list.