It is possible to employ some of the principles of classical and operant conditioning in a program of self-directed behavior modification. You begin by choosing one problem to modify. Then you spend a week or so keeping a diary or journal of your normal behavior. The contents of this diary constitute the baseline data you will use to determine what aspects of your behavior need modifying and what actions and feelings that contribute to the problem may be susceptible to behavior modification.
In this baseline data, you must include every instance of engaging in the target behavior, with entries indicating all the factors at work while you ate or smoked. You'll want to know how much you ate or smoked, whether you did so alone or with others, where you were, how you felt before, during, and after, and any other factors that might be related to your behavior.
Checking your completed baseline data, you may discover that certain people, situations, or feelings seem to be cues or stimuli for your target behavior. By using the behavior modification technique of stimulus control, you can begin to master the forces compelling you to engage in the habit. If, for instance, you find that you eat too much when you are out with others, control that stimulus by removing it--eat alone. Similarly, if you seem to smoke most while watching television or reading, confine your smoking to other occasions.
You can support your stimulus-control efforts with a program of rewards or reinforcements for meeting certain behavioral goals. If you are in fact able to, for example, restrict your eating only to mealtimes and only to the dining room, give yourself some predetermined reward, like the purchase of a book or an article of clothing. You can even set up your own token economy by awarding yourself points that add up to rewards you can collect later. You can keep track of the points by carrying toothpicks or similarly portable counters in one pocket or part of a purse and transferring them to another spot as you meet some behavioral goal you've established as worth a certain number of points.
You can also alter your actions behaviorally by changing the sequence of events, doing things in a novel order and thus disrupting the stimulus-response pattern that may be sustaining your target behavior. And you can employ incompatible behavior, whereby you do something else, rather than your target behavior. For example, if you always seem to bite your fingernails in certain places at certain times, you can weaken the habit by becoming aware of the situations that reinforce it and by arranging to have something in your hands on those occasions (thus acting incompatibly with the habit).
The success you achieve with self-directed behavior modification depends largely on your willingness to go slowly and stay with the program. You have to keep complete baseline records, consistently use the chosen technique--failure to do so every time, and as soon as your target behavior is manifested, can make your problem worse than before--and try to concentrate on one problem at a time. Make sure that you understand the basic principles of behavior modification before you begin your program, try to keep your goals obtainable, and you should have success in modifying your behavior.