It's like a pilot's first solo flight; just as any landing you can walk away from is a good one, anything that starts cleaning the toxins and garbage from your body is helpful.
I've been taking regular enemas for many years, and have reached a point where one every 10-14 days seems about right for me.
A few tips.
Treat the exercise as just another part of normal personal hygiene; you probably brush your teeth regularly; nothing wrong with paying attention to the other end. I usually take an enema just before bathing.
Make yourself comfortable; spread some old towels on the bathroom floor and bring something such as a folded towel for your head.
Lie on your back, and try to find a nozzle slightly smaller at the base than the business end. This will free up your hands to massage your abdomen.
Once the nozzle has been inserted for the first time, expel at the first urge. No sense pushing the oldes residue at the bottom back up. When that's out, refill the bag and try to take more and hold it longer.
At the first sensation of pressure, take a deep breath and hold it for just a moment. When your diaphragm relaxes, the solution will probably advance further; the pressur in your rectum may move up below your ribs.