Before you run, you must learn to walk... same as before you become a Sales Trainer, you must be a do sales first. Like they say, u must know the selok belok of the trade before you can train people. You can learn very fast in sales by joining usj forummer in their MLM
Look for an industry of interest to you, start from the bottom then work yourself up.
The most important thing is you must be able to talk, fluent, express your thoughts, express your feeling, convince people and read alot to do that. etc.
Self Development? Maybe u should try to enter as HR first.... most corp like Tenaga, Telekom and JKR do have their own training section some, their own Univ.
Good luck!