The easiest way for me to cut down on my use is to just ride out the storm. I'll usually find a drug that I absolutely love, use the fuck out of it, and move on, vowing to use it only on occasion afterwards.
In a nutshell, I don't really avoid becoming addicted to things, I just learn from each addiction to avoid such instances involving each substance in the future.
It works very well, and can offer a tint of maturity to the drug-user; obviously, it's not mature to allow oneself to become addicted to anything, period! But once you do become addicted and have that built-in mechanism by which you are psychologically inclined to quit and remain abstinant, save for on occasion, I feel one gains experience that will eventually help them (me) later in life.
one becomes much more knowledgable about the extremely positive and extremely negative effects of the drug in question, and is therefore able to rationalize about their use in the future. Just my opinion, but its worked wonders for me and I dont use seventy five percent of the drugs I was addicted to anymore, based on this philosophy.
LOL however I'm not advocating addiction as a means to abstinence

Just relating my personal experience.