create a goal in Google Analytics. If you are using AdWords, you get a code to paste on the page where conversion is finalized. Paste it and track everything. Also, take some feedback from your customers
Your question is not clear. What you are asking for, a checking method for present keywords that are bringing business for you or you need some ideas to make such keywords?
There are tools that helps find high converting keywords like word tracker, google adwords, spyfu or keyword discovery.
Try to analyze the keywords of your top competitors what keywords they are getting conversion from?? Generally high competitive keywords work well in conversion, so keep checking keyword research tools..