If you stop and think about it, online advertising is only one method. Offline advertising offers several more methods - newspaper, magazines, radio, television, brochures, mail and billboards. The Basic Have some business cards printed and make sure you have your web site URL in there. I know of an individual who started a small ISP business offering dial-up access. When I asked for a business card, the guy had none and just wrote down his number on a small piece of paper.
Nothing can be more careless than that.
The importance of having business cards cannot be emphasized enough. You can forego having a cell phone or a pager but a business card should never be off the check list. Along with business cards, you can also include your web site URL on all other printed office supplies you use. These include stationery, brochures, invoices, receipts, etc. One of our local pizza delivery places even had their URL on their sachets of hot sauce and ketchup.