How a man can improve his ability about sales?

good luck for the job...................  TRY YOUR LUCK ,,, INSHALLAH YOU WILL GET IT ,,, APPLY AS MUCH YOU CAN ON THE VACANT POSITIONS ....................  

Start by improving your English skills if you will be speaking English in your sales position.

Secondly, try to follow / shadow a sales star during a normal day to see and learn how she or he interacts with her or his prospects. You will learn a tremendous amount by simply observing someone good doing what they are good at.

Finally, start reading books on sales skills. There are numerous out there. Also watch youtube videos on sales.

Trying to sell.

i.e. selling cake in the street is the hardest and remain the best school

Then for largest position in sales education is needed to understand product, to understand law, logistic, company results, customers, market... but my advise would be to start as young as possible.