The suggestions above are excellent and helpful.

I've seen a practice grow from 800 clients to 2,000 within five years thru word of mouth by giving the existing clients discounts whenever they refer a new client. The discount only applied in the first two years and the other three was purely from word of mouth only. The volume is unusual but at least you can get an idea how effective discounts are. This practice is about 25 years old.

I've also seen another practice that grew from 300 to 800 clients within 10 years by word of mouth only. This office has been in practice for 20 years.

I'd say you'll peak by the 20th year. Meaning you'll have more clients than you know what to do with if you manage it wisely. Your practice will probably be sustainable at most by the fifth year.

Make sure your client folders that you give to them look good and professional.

Eventually you'll find your niche and many clients will go to you for your expertise.

If you do bookkeeping, your clients will usually ask you to prepare their taxes as well. Corporate returns are one of the most profitable returns because you don't need to meet the client because you already have their bookkeeping data. Plus they'll ask you to prepare their individual returns and maybe their kids' as well.

Giving the clients the option to buy audit insurance is gaining in popularity. I've seen the fees range from $100 to $500 per return. The $100 is for a $425 return and the $500 is for a $600 return. The caveat for the highest fee is that the guy prepares his returns aggressively with bogus numbers and is in the IRS office every other week. Natually, the clients think they're getting a good deal since they are audited more than is normal. The $425 returns were prepared conservatively so the ratio is 1 audit per 500 clients.

Audit fees are usually around $500, depending on the complexity. First you meet with the client to go thru their receipts to let them know what else is missing. Then go to the audit without the client because they may volunteer info that'll prolong the process unnecessarily. I've been told that the auditor doesn't want TMI, especially one who is about to retire. Some IRS offices are more relaxed while some are pitbulls. So giving them only what they request is best and know what documents they are allowed to ask for and which ones are not. 

CPAs charge the most for returns. I've seen EAs charge $500 for the same $1,200 return prepared by a CPA.

Having a website is mandatory. You could include a worksheet that the client can print out from your site. The purpose of the worksheet is to make it simpler for the client to list their expenses. This is the area they procrastinate most.

A lot of clients will ask questions off-season. If it is a simple question, consider this as gratis PR work. Believe me, it's better than advertising. Most of the time, it'll be about the independent contractors will ask about their estimated tax payments based on the income they've earned so far, buy vs. lease autos, how much mortgage can they afford, and what should be their W-2 withholding.

Finally, don't forget to buy an E&O insurance.

I hope this helps.