After I-130 is approved, the case goes to National Visa Center. They will ask for other documents. Birth Certificate, Marriage Certificate, Visa Application from your wife and Affidavit of Support (Sponsor). In this document you, by yourself or by having co-sponsor, need to prove you have 'sufficient income' to support the intending immigrant (your spouse). The income may vary by state, and has to be at least 125% of poverty level for that state. It is approximately $20,000 for family of 2. That is you or co-sponsor need to have earned and paid taxes on at least $20,000.

Hope that helps