I think the aspects of focus and the mental techniques have been pretty well covered, let me talk about the physical form, according to some the only truly important aspect of it, and according to others the least important part. Who's to say who's right?
Try to use a mirror, a tall enough mirror to see your whole body sitting, and put a string with a weight on the end of it directly in the middle of the top of the mirror and as it hangs down it should be a perfectly vertical line. Perfectly plum. Try your best to be completely symmetrical and aligned with that string, and check your posture constantly. The posture IS the enlightenment, is what a Roshi once said, and this is a great way to practice your own posture without a master of meditation showing you the ropes. Tuck your chin in, push the top of your head to the ceiling, shoulders down and relaxed, keep your eyes slightly open and fixed on a point, or closed and visualizing, or open and visualizing, or closed and stuck on a point. All 4 variations have something to offer. Push your belly slightly to the ground with your stomach muscles as you inhale, and every now and then, when you exhale, exhale so thoroughly that you completely empty yourself of all breath, then take a very deep breath, then return to normal, counting your breath all the while, and put those extremely deep breaths in at irregular intervals. That tends to get your body out of a simple hypnotic repetition, and challenges your mind a bit more. Plus the exhalation has been very important in "achieving" samadhi. Many people say that keeping a wry smile, a slight smile, while meditating adds another dimension. Try that! Smile even when you aren't meditating, and have no real reason to smile, just smile to make yourself feel better and at ease. Your behavior controls your feelings as much as your feelings control your behavior.
Do an exhalation before you start counting, that is like your primer. Some people can fall into a state of samadhi with just that one exhalation, masterfully done. Practice that, keep doing it.
The key is to meditate until you "reach" enlightenment, then keep meditating, then keep meditation after that. That is the original Buddha Nature.
Or something...idfk