Hatha Yoga though apparently upon first glance seems innocous enough it is essentially the last yoga. The Full corpus of Hatha Yoga is, if I may use an analogy, like doctorate work.
You may take from Hatha Yoga the flowing asanas and perform those postures, as in Surya Namskara and the various asana sequences put together such as Bikram, power, ashtanga vinyasa and so on. Practice of these postures is of significant benefit and can be practicely relatively safely once properly instructed.
Even alternate nostril breathing without locks, and without much in the way of strain spent holding the air is of benefit and little danger.
Alone and unguided by reading all the texts we start hankering after abilities and extraordinary experiences. So we disregard the rules, skip around, we start trying this mudra, that kumbhaka, concentrating here and uttering that mantra and suddenly we find ourselves in a bit of trouble. Sometimes big trouble.
I can not stress enough the importance of a genuine teacher who knows what the hell he or she is doing. If no live teacher can be found and you want to persist in this business, although I don’t recommend it, then the best I can say is “Go Slow. Not Fast. Take your Time. Follow the rules. Don’t skip around. Slow careful step by slow careful step. Be cautious.”
My advice to the original poster is this:
Give up all intoxicants.
Be moderate and sweet and sattvic in your diet according to your contitution.
If flowing yogasana is pleasureable for you I would take that up.
If alternate nostril breathing without locks and strain can be done pleasantly I would take that up a little.
[I]The final, and most important advice other than the first two is to take up the Pranava as your sadhana[/I].
Contemplate it. Read and Learn about it. Ideally get initiated into it, and most importantly once you have a grasp on the whats, whys, and hows - you should sit and utter it.