Get a clip on macro lens for under 20 bucks on amazon. Limit digital zoom when possible. Lighting is key and light box can do wonders. Try neutral backgrounds of white or gray when possible. Lots of light on fly helps.
On FlyFlasher.com you can find 32,832 flies from all over the world. Flash your own fly patterns, upload your current work or search for inspiration. The flies are tagged, so you easily can search for them.