It amazes me how many people ARE NOT doing this, so….
1) Have an online business (or storefront)
2) Automated systems to sell your products?
Then you need to be investing in automating your business growth.
How you say?
1) Google Adwords / Yahoo Search Marketing: capture people already motivated in your product and sell to them.
2) Search Engine Optimisation, after above run a Search Engine Optimisation campaign to garner daily free traffic to drive sales.
After three months you will have a fair idea on growth off that and do exactly that. Grow.