Dallas and Geoffs make some very good points. I found that procastination was my biggest enemy. After all who really wants to look at all of ones faults, likes, dislikes, any other character flaws we have aquired in our drinking and non drinking carreers? The best thing about this step is that you don't have to look at just the bad things, you can also include your good points.
I have a quick story about the 1st time I did a 4th step. I had been putting it off for several weeks, and one night I got a call from my sponsor, around 8 pm. He asked me how I was doing with my 4th step? And keeping in mind that I had just completed my 3rd step, I told him that I was working on it, that I was turning it over to my higher power, I was leaving it in MY God's hands, and have it ready in His time. Pretty clever, Huh?!? So as we hung up the phone, I figured I had upset him, but that was OK, I'd repair the damage later. I went about my business the rest of the evening. Somewhere around 11 - 11:15 that night, after I had gone to bed, the phone rang, it was my sponsor. He informed me that he had just had a chat with "Your God", and he had told him that I would have my 4th step to him be 10 am the next morning!!! So when I met with him at 10 am, I had completed my 4th step!
I found that it wasn't near as bad as I thought, and as I discovered the longer I am sober the "more that is revealed", so although the 1st 4th step wasn't as thorough as it could have been, I always have a chance to do it again. And I do, every year I do another 4th and 5th step with my sponsor, and each one is more thorough than the last. You see, it is impossible for me to remember everything that happened in my life, especially my resentments, fears, and harms, I, like everyone else here, drank to cover these things up. The main thing is that you be as Honest as you can, and stay sober in the mean time.
Good Luck, you won't need it, but by all means don't procasinate.