My rig:
Canon 40D
Canon 100mm f/2.8 Macro USM
Canon 430EX
DIY Lumiquest Bounce (made from craft foam)
The brands and models are not important, just that you have the functions
Goal: You want to expose the subject (flower, bug, etc) with the flash. You want to underexpose the ambient background, so they colors are vibrant. If you underexpose the background and correctly or slightly overexpose the subject, then the subject is going to "pop" off the bg. Also, the colors are going to be stunning.
It's exactly like taking a high class portrait with lots of off camera lighting, only on a smaller scale.
How it's done:
1) 430EX in ETTL. Flash head at 45 deg. I generally dial in +1 FEC (Flash Exposure Compensation)
2) 40D generally in Av*
3) I set ISO to 200 or 400
4) Be sure you have enough DOF. I generally start at f/8 with these shots and move up (f/11+) if needed. Remember the closer you are, the less DOF.
4) For fast moving subjects, I like AI Servo focus and I use higher fps (but remember the flash has to catch up
5) CHIMP!!! Don't be scared. You're trying to balance two light sources (flash and ambient) for a great shot you need to be sure both are working how you want them to be.
* I set my custom function for "flash sync speed in Av" as 1/250"", not auto, so when I shoot in Av with flash, I'm shooting 1/250" shutter.
Making it easy: I find macros with flash are way easier than without.
1) You generally do not have to worry about shutter speeds (only for ambient light)
2) You can use lower ISOs = less noise
Troubleshooting:
Subject underexposed: dial up FEC
Subject overexposed: dial down FEC
Background overexposed:
1) In Av, dial down EC (camera exposure compensation) or
2) Lower ISO or
3) Use M mode, lower shutter speed (less than 1/250")
Background underexposed:
1) In Av, dial up EC (camera exposure compensation) or
2) Raise ISO or
3) Use M mode, raise shutter speed and turn flash HSS (high speed sync) on
Technical (why it works well):
The importance of the DIY bounce is twofold: 1) Softness. The size of the foam turns your flash into a larger perceived light source (huge source relative to your subject). Larger perceived light sources = softer light = easy shadows. Shooting flash off of white foam creates diffused light, not direct reflections like silver metal. Look back at the examples and see how the shadows just fade away instead of being sharp?
2) Direction. The flash head is at 45 degrees. The DIY bounce does bend forward also, so the flat foam surface is almost parallel to the lens. When the light bounces off the foam, it goes DOWN onto the subject. It's an off axis light. This creates some shadows, depth, and a 3D look. However, the shadows are not too dark because of the large light source is so diffused.
On axis light (aka a ring light) does an amazing job of fill light, but does not give depth.
Get shooting and good luck!!!