Once someone has promised you something, they should deliver or tell you "no" to your face. Until either of those things happen, we follow a strict pledge chasing system. We follow this system strictly because pledge chasing is psychologically taxing. These are often your friends, after all.
We recommend a 10-7-5-3 pledge chase routine. After a promise, send all of your immediate requests. Then wait 10 days. After 10 days, contact them again. Then wait 7 days, and contact again. Then 5, and then every 3 days until their pledge is fulfilled.
You can make each contact different, but all of your messages should always emphasize your viability and the urgency.
Don't stop until they tell you no.
Deadlines are one of the most important tools in fundraising, whether you are talking about a public reporting deadline when running for office, or a deadline you set at your nonprofit. This is where you'll go all out — call multiple times in the same day, offer to personally pick up or courier larger checks, etc. Get every dime you can in before the deadline. Three days before a deadline you should pause any other calltime you are doing and...
There are many ways to do it.
Who you need to contact on what day