Once your fixed braces have been removed, you will need to wear a retainer to make sure the teeth don't move back to their original position. You'll probably need to wear the retainer for around six months - all the time at first, and then probably just at night. Your orthodontist will tell you when you can make this change - don't be tempted to reduce your wear of the retainer yourself, as this could have an impact on your treatment.
Brushing your teeth twice a day with a fluoride toothpaste and keeping your diet healthy is important whether you wear a retainer or not, but you should be especially aware of cutting down on sugary snacks and fizzy drinks, as these may case more damage to your teeth while you are wearing your retainer. You should take your retainer off when you brush your teeth but make sure you give it a clean too to get rid of any old food. If you are using your toothbrush, though, do be careful not to damage the retainer.
Even if your brace is removable, you should still wear it for the amount of time recommended by your orthodontist. Don't be tempted to flick it in and out as, not only will this not help your treatment, it may also damage your retainer.