When you want to make money with Twitter you need to first think about the specific niche you want to target. Your tweets should be about the specific niche and allow your followers to get to know you on a personal level.
Once you find your niche you will need to find products or services in which you can sell to your Twitter followers and recommend. These will be your income streams and a good rule of thumb is to find a product that has a recurring commission.
Making a income with Twitter is much like doing e-mail marketing. Except for long sales copy in which you use for e-mail marketing you will instead be using small incentive treats of 140 characters or less. Come up with compelling headlines and something target specific that many in your niche have a question for. By creating articles and linking to them with specific questions being answered out your niche you can improve your conversion rates.
Also consider networking with your followers by sending them direct messages and direct tweets. This will show others that you are active within the current niche and build a trusting relationship with them. By building a trusting relationship you increase your profits along with a chance of your followers becoming repeat buyers.
If you need some quick followers within a specific niche consider looking it up on Twitter networks were doing a keyword search within Twitter itself to fine users talking about your topic. Follow a number of these people to create your starting base.