Here is a common cycle of self-employed retirement accounts -
1. Not profitable yet, and either not contributing to anything, or is through an employed spouse's 401k (or similar)
2. May not be profitable, but have some cash or realize closer to retirement and getting scared. So, if your tax rate is low (i.e. zero), then a Roth IRA is a good option because you are getting taxed at the time of contribution (i.e. zero%). This assumes your income at retirement will be higher than now.
3. Starting to be profitable, but still not great. Maximize a regular IRA contribution and use the additional catch-up amounts if you are over 55. Now, this does two things for you, first you are contributing to your retirement and secondly, you are reducing your AGI on your tax return, therefore reducing your Income taxes (not Self-Employement tax).
4. Once you have a decent profit, you can open either a SEP IRA, Simple IRA, or Solo 401k. These are also great ways for people who are self-employed who may have large fluctuations in income year over year, such as realtors, etc. Each has different timing rules, funding rules, but the best thing is that you can make a much larger contribution to your retirement fund, and at the same time, be able to reduce your AGI on your tax return, therefore your taxes.
This is when it really helps to work with two advisors closely - a financial planner who understands self-employed needs and a tax preparer who specializes in business. These two people will work together with you to help you to maximize your retirement, get the best tax benefit, and if you have employees you can still help them out as well. It's important to note here, I'm talking about just a $5000 contribution to your retirement, under some plans and having met the qualifications can be upwards of $50,000 in one year.
Also a benefit to the plan types in #4, is that some can allow for a loan to be taken against retirement funds that have been previously contributed. And when you pay it back, you are paying yourself back the interest.
All of the options above can be powerful ways to really keep hold of more of your money for the future, reduce taxes, etc.