Brushing alone misses the sides of the teeth where they touch, and that is where gum disease and much decay begin. Clean between them once a day.
Small interdental brushes are the easiest for most adults with gaps. Floss works better where the teeth are tight. Water flossers help people with braces or bridges.
A little bleeding in the first week is common and usually settles as the gums get healthier. If it does not, tell your hygienist.