Firstly, the upper and lower teeth should be brushed separately, not with an up and down scrubbing action. (if you brush like this you will miss the crevice around the gums). As mentioned before, the lips, cheeks and tongue are major obstacles in the effort to reach the gum line.
I suggest you start at the hardest to reach place first i.e. the lower, inside (tongue side) molars, at the back of your mouth. Try to place the brush head half on the gum and half on the tooth. This is actually a very small area but you should be able to feel the bristles on the gum. Please scrub hard! Your tongue has a mind of its own and you will fight the toothbrush without realising. If you gag, I'm afraid you will just have to try again. This is why a small head is the best choice. Rotary brushes are excellent because you never scrub with them, you just press and hold as the battery does the work for you. When brushing the inside of the FRONT
teeth hold a manual toothbrush vertically and scrub really hard. Lingual calculus forms very easily here because most people simply don't brush hard enough.
PLEASE NOTE
many people are scared of over brushing and causing gum recession. Gum recession is caused by factors such as the thickness of the alveolar bone and the body's natural susceptibility to inflammation. If a person brushes timidly for fear of recession, this is more likely to happen in the long run anyway. As the great saying goes "It is better to be long in the tooth, than to have teeth no longer". Most recession occurs on the outer surfaces of the gums (side which touches the lips) and I suggest you use small circular movements on these surfaces. Try to angle the manual brush at 45 degrees to the gum margin.
When brushing the upper molars keep your mouth relaxed. Your jaw muscles have 4 sets of muscles. 2 of these muscles open and close the mouth. If you open too wide or clench too tight there will be no room for the toothbrush. Try it for yourself; put the brush by your upper molars and open your mouth wide. I guarantee you will struggle to reach the gum line. Then clench your teeth tight, you will feel the other muscles working. Most people don't think about what they are doing when they brush. It is a good idea to watch in the mirror and ask yourself "Am I reaching my gums?" If you aren't, then your mouth will still be dirty.
So to recap, I scrub the inside surfaces of the gums and circulate on the outside surfaces of the gums, always top and bottom teeth separately. I hope this is helpful.
DO NOT AVOID BLEEDING GUMS..... THEY ARE UNHEALTHY!