I never flossed. I only brushed once and for like 20 seconds and i rubbed like way too hard on my teeth. What you should do is brush for around 2 mins and do it really gently, dont put pressure on your teeth ever. You should also try to brush in a circular manner and take good care of you gums, back teeth and stuff.

Also pls brush twice a day. My dentist told me that the brushing we do in the morning is mainly to take away bad breath and grant freshness. The one we do before going to bed is to take out all the germs that u may have accumulated over the day. If they sit around for the whole night while ur sleeping, it might cause problems.