In order to ensure that you stay on track with your weight loss goals, there are several things that are worth tracking. By keeping an ongoing record you can trend your results and determine whether you are succeeding or not easily.
Here are the ones that have been particularly useful to me.
Weight : If weight loss is your purpose. (or gain)
Muscle Mass : Tracking muscle mass in relation to body fat percentage and weight is very helpful especially as you get closer to your goals.
Body Fat Percentage : It is a universally accepted measure for how much of your body mass is fat. Ideal numbers are different for men and woman. Irrespective, this will prove an overall indicator of your success, and will be very helpful when making decisions about exercise and diet.
Base Metabolic Rate : This tracks the amount of calories your body burns in a resting state. It is helpful for working out the correct diet / exercise combination to ensure that you maintain just the right sustainable caloric deficit. If you know what your base metabolic rate is and you know what you caloric burn is for the exercise you do, you can easily adjust your diet to the right level, to create the right balance.
Physical measurements : Fairly simple if you are just focused on loosing weight. Use a measuring tape. Getting closer to goals, I have found measuring tapes rather unreliable and not very helpful. I like taking photos (selfies) at regular intervals (every 6-8 weeks.) Easy enough to compare, and see your results.
Food : Knowing what and how much you eat is useful for making sure you maintain the right balance between food and exercise. Since results tend to develop over time, I have found it particularly useful to keep track of my meals. When I make dietary adjustments, for whatever reason, it is easy to see whether a change actually has an affect or not, especially when done in correlation with the other factors tracked.
Training : Knowing how many calories you burn from which training sets, and which training sets you do, historically tracked, will make it possible for you to trend results as well as determine whether changes have had an affect, and what that affect was. Positive of negative.
You cannot track what you do not measure, and if you do not measure, how do you know if you are successful or not?
Measure. Track. Adjust. Succeed….