Cold turkey on caffeine - takes about a week and a half to get over the addiction and you'll be sleepy and have headaches for most of it.
After that you'll be perkier than before and will probably even sleep better (depends on how late your last caffeine intake of the day was before as it mainly works by you feeling sleepy earlier and naturally going to sleep earlier).
You can still take something caffeinated once in a while and you will really notice the effect of it once your body isn't hooked on the stuff (just don't to it too often or your body will go back).
You see it turns out that when you're addicted to caffeine you actually require regular caffeine intakes merely to be at your normal baseline level, and will be below it without the caffeine, whilst for those who are NOT addicted to caffeine taking it actually umps them up above baseline (I once read of a study about it but don't have the link anymore).
If you actually like the taste of coffee and the coffee habit as I do, switch to decaf. If you have hot water at work, buy instant decaf and make from that yourself.
If can't be added getting over the caffeine addiction, do you can use instant coffee instead of instant decaf.