I've done about 3 rounds of P90x and have done quite a few of his 1 on 1's. For the last 2.5 months I've been doing P90x+.
Some have already stated it, DON"T MISS A DAY! Stick to the diet! When you miss a day repeat the week over. If you repeat a week over twice, start the round over again. That was motivation for me to not miss a day. It's hard to create a good habit and this is a good one.
I lost about 25lbs in the 1st 90 and have leveled out intentionally. I can see muscles I haven't see for years. I'm not quite as trim as I was after the 2nd 90 days but I'm content with what I eat and how I look and feel.
There is another thread on here with probably 12pages of p90x stuff.
At the end of the 1st 90days you'll feel like you really have accomplished something.
I also recommend getting on the p90x web site and learning more about diet and others successes and failures. The other thing I'd recommend, if you haven't done so, get on a web site that helps you count calories. This will help you understand appropriate caloric intake as well as your carbs, proteins, and sugars. I used myfitnesspal.com Finally, track your workout progress or as Tony says document it. There are several spread sheets available online. This helps you see your progress and challenge yourself each week.
Oh, and Tony's best on mute.
I use mynetdiary.com. It has a nice mobile app and a great iPad app.