Make sure that whatever product or service you are offering is of the highest quality.
Understand your customers needs and expectations and then exceed them.
What he said
Make sure that what you are offering is of top quality.
Then make sure you are taking advantage of the paid and free bumps.
I have also found that featuring my service in it's category for a month has really helped me to get my initial sales going.
Make sure that you are responding promptly to customer inquiries about your service and actually answering their questions.
Once you do get a sale, make sure that you over deliver ahead of schedule. Also provide a high level of customer service, and go the extra mile to make sure your buyer is truly satisfied.
This will help you generate repeat business, and word of mouth.
You do not need to have huge amount of investment for a business, but you need to have relevant idea for amount you have.