In thinking of a self-control habit for your child first think and ask them about things they enjoy doing. Don’t think of asking them to develop self-control by not doing something. Keeping in mind all the time to not do something takes more energy than thinking of doing something in a certain time frame.
Setting Up a Model for Self-Control
Set it up a specific time and place in which you ask your child to commit to do something for a short 15 minutes on a regular basis. . Psychologists like to call it the "IF" and "THEN" model. It means that if “if” is now 5 pm "Then" it is now time to read my book or do my homework.
What the child chooses to do can be reading a book for 15 minutes every night after dinner, doing homework for 15 minutes at or even practicing music or art.
When you are setting up this model for self-control it is also a good idea to describe it as the time when your child shuts down the TV or computer game and puts in the time for that something lese. It is the something else (reading, art, music) which is important, but shutting down distractions is an important byproduct.
It is best to explore with your child what that something else should be. That something else your child is doing should be educational and a little challenging. It means they are working on developing a skill.
It can be anything from music art, or even athletics. The important fact is that they should focus on improving in one of those areas and practicing. Practicing takes self-control and discipline. What you don’t want is to allow them to assign this for an activity which is just fun and relaxing. You child will not learn self-control from that.
Remember that this self-control muscle works like all other muscles. That means it takes your time, patience and discipline for you to implement it and teach your kids.
Hopefully your motivation in knowing how important it is to your child's future success will give you the strength to persist.