If you wear a pair of jeans more then it will loosen around your waist. The loosened jeans can be fixed without wearing a belt.
To fix the jeans, you need a elastic strip and a pair of sewing machine. You need to use the sewing machine to fix the jeans.
Make your jeans tighter at the waist
How to rip your own jeans
You can put on the jeans and mark the spots which you want to rip with the help of pen.
It is better to rip at knees and lower thighs. If you are a teenager then it is fashionable to have ripped jeans.
You can take a grater from the kitchen and rub it over the jeans. It is much more easier if you are wearing it. It is better to grind the jeans where you want to prefer the look i.e. the best spots are the places where your jeans get strained: the knees, back pockets and hips.