Teeth should be brushed at least twice a day for two minutes at a time. It's usually best to do this as soon as you get up before breakfast, and before you go to bed. You should avoid brushing straight after a meal or after drinking sweet or acidic drinks like fruit juice.
You can find more advice on brushing your teeth and keeping teeth and gums clean and healthy at the NHS website.
If you have problems with your hand coordination or grip, you can get specially adapted toothbrushes with handles that will help you. Some people also find electric toothbrushes helpful as they reduce the amount of hand movement needed.
If you have problems with your vision and find it difficult to see what you're doing when brushing your teeth, a good bathroom light and a magnifying mirror might be useful.