". . . Can you please explain me how can some one improve his credit score for quick approval . . ."
That will depend upon what the cause(s) of the low credit score.
If it's an excessive debt to income ratio, that's hard to rectify in the short run, begin by ceasing to create more debt;
If it's late payments, then someone has to begin habitually paying their bills on time, or ahead of the due dates;
If it's delinquencies where the applicant has demonstrated an intent to simply abandon his/her responsibilities to service the debt, then contact has to be made to establish a re-payment schedule, and then perform.
Some people simply have too many open credit cards, and even if they have ZERO balances, that represents "potential debt", and 50% of each card's limit, or so, will be counted (by formula) as actual debt. Cancelling credit card accounts will become a necessity . . . . but closing accounts hastily will also have a short term negative influence on the credit score, and may take 3 to 6 months before it ceases to play a role in the calculation. As a starter, the applicant must STOP opening new accounts.
Nothing is "quick" but it starts with identifying the underlying cause(s) of a low score, and then methodically addressing it; but no one else can do it except the applicant.