I massage the area I'm going to inject for a couple of minutes first. Then, I heat my redijects up under warm water, then inject with a 25g pin. It takes awhile to shoot, but it also makes the injection go alot slower, which can help. Afterwards, I'll massage the area for a few more minutes, and then if I'm going to sleep, I'll put a heat pad on it. I've never had any type of pain, just a very minor sore area if I touch it when I do this.
More than half the time I don't do this, and I'm sore as hell. If I inject my quads, I'll have a limp for two days. My next cycle I'm going to take the extra ten minutes for every injection.