If you haven't seen the ammonia rise after three weeks, then try adding the shrimp to jump start the cycle. From there, just wait until you see the ammonia levels rise and then drop back down to zero. Then you can try a relatively hardy fish.
Some good fish for beginners that you will want to research while you wait for the tank to cycle are: damsels (these get mean and then even more mean as they age, but they are very hardy and will survive most major disasters in your tank), clownfish, grammas, several members of the blenny family (bicolor blennies are neat, but do read about these first and know what you are getting into!). Also check into the neon goby and the watchman goby. Neon gobies are not terribly long-lived, but my goodness are they cute and sturdy.
I would add fish only after the tank has cycled. Let me say that again, AFTER the tank has cycled. If you haven't seen an ammonia spike after three weeks, and the shrimp are not helping to jump start the cycle, then please post here and ask for help before you do anything else!
You want to start with the most peaceful fish and add more aggressive fish last. This way you can ensure that your more peaceful community members are established and less likely to get picked on by the more aggressive fish in your tank.