I'm assuming you are British. Are you working? If so, you need to include evidence of such; payslips, letter from employer, bank statements. If you own your home, then the mortgage. If you are renting, include the lease and make sure it's on there that your wife has permission to live there if she isn't named on the lease.
The main thing is to show that you can support her without relying on public funds. So any savings would also be beneficial to include in the application. If finances are tight, include a detailed budget. There are quite a few on here who have posted pretty detailed lists of what they provided with their applications; try doing a search through previous threads, it could be pretty helpful.
Congratulations on getting married!