One of the things that has made the biggest difference in helping me to be mindful of what I eat is keeping a food log. This is pretty much standard practice if you see a nutritionist or dietician. Initially, I started keeping a food log a few years back to get a handle on my caloric intake when I was trying to lose weight. These days, I log somewhat frequently to make sure I'm eating enough to keep up with training, and that I'm getting enough nutrients.
What you can learn from logging you food, assuming you are honest and fairly accurate, is a whole lot.
Logging your food allows you to get a sense of portions, caloric density in various foods, the diversity in your diet, and the general nutritional soundness of your diet.
I find it particularly useful for tracking trends in nutrient deficiencies in my diet and correcting them. For example, I tended to be a little light on zinc and vitamin E over the course of several weeks, so I was able to alter my diet to include more foods rich in zinc and vitamin E.
Also, during peak training periods, the log helps me to understand just how much I'm eating versus how much I need to eat. Sometimes I find it too easy to not eat enough when I'm already fatigued from hard blocks of training and the log reminds me, yes, I need about 5,000 calories (!) on those hard days.
I like fitday.com a lot. It's free. It allows you to add custom foods. It's pretty user friendly.
Fitday also allows you to keep track of your exercise... one caveat... it grossly overestimates calories burned during exercise. This is true for most online exercise calculators. I train with a PowerTap and use the Kj expended as my guide to calories burned (because of our body's efficiency 1 Kj equals roughly 1 Cal) .
Some folks don't log their exercise in fitday for this reason. I still like to keep it all together so I can get a sense of calories in and calories out. I end up tweaking the average speed of my rides when I enter them to get a more accurate caloric expenditure number. It looks like I'm doing a lot of 12-13 MPH rides, but I'm not. I'm just a whole lot more efficient than the calculator assumes I am.
My log lives here. I've been bad about keeping it updated, but I'm working on it:
Mark's food log
It may be tempting if you think you need to lose weight to use the food log as a means of restricting calories but don't do that. If the whole point of training and eating well is to make yourself faster, why risk your health and fitness by overly restricting (over 500 calories a day) your caloric intake?