Consider Source of Lead
Start with considering where you met the person you want to sell your product or service. If you have just picked a company from phone book, this can be a less promising lead than someone you have met at a conference or trade show. Better work on the lead that you have found through a contact and talking to a person.
It is possible that someone sounded to be a promising lead for your product as far as buying of your product or service is concerned. So contact the person now. Sometimes, the people you have maintained a regular contact with can give you more successful leads. You should be spending more time on them.
There are many specialized software solutions through which you can search and work on the leads. Install any of the softwares and then search the leads. Working on new people is rather difficult but you must pursue them. Do not ignore new leads altogether; with a little bit work on them, you can turn them to be promising ones.
You should regularly attend conferences and seminars in your niche area, and exchange visiting cards with businessmen attending. You can then contact them later on and talk about your product and services. This is an effective way to develop contacts and turn less promising into more promising leads.
It is possible that someone is not willing to buy your product or service at the time you requested them, but promise to consider it in the future. A better way to keep such leads intact is to maintaining of regular contact with them. If you have talked to someone before less promising, talk to them again. They might be interested to by your product or service now.