You may want to try the 7-day course “Why (oh why) can’t I breath properly?” before embarking on traditional breathing meditations.
This course explains how the breath can be tricky.
The most important thing is to go slowly, discovering what helps you. Speaking for myself, many times the breath is a no-no. Sounds or the feeling of my bum on a chair are much more helpful. It all depends on the day, and on my mind-state.
Download Tick Chart PDF