Two really good websites which will give you all the information you need. The first Catherine Cavanaugh's "How to give yourself an enema" has all the basics.
Like you I started enemas thinking I should try coffee ones first. This wasn't so good for me. Even my colonicist advised that I should just stick to plain warm water enemas to begin with. But my constipation isn't caused by a sluggish colon, I have strong peristaltic movements and the coffee was too much for me. The first coffee enema was very pleasant, soothing and peaceful. Then agitating....
It is worth noting that the advice for coffee enemas is actually to use a small amount of water/coffee mix. Just a pint of liquid. A coffee enema is not supposed to travel too far up the colon and is used as a "medicinal" enema. A plain warm water enema is usually a litre/two pints and this is the minimum amount to clean out the colon. Some people can take more water. I can't. My colonicist says I can take very little water compared to other people.