Dania,
I'm not a CPA or Tax expert but, I am a professional photographer (a small business) just as you are. What you need to do is track all income. You're starting a small businesss, which makes an income and has expenses: marketing, travel, office equipment, administration materials, etc...
You need to keep in log (generally your calendar) all of your appointments, bookings, travel everything. That's part of your expenses, which off-sets your income. NOW some things to remember. Always put into a savings account or some separate account 25% of what ever you bring in and pay that toward your taxes, otherwise you may have to pay taxes. Or, you can do as many small business people do...risk it and hope that your expenses off-set your income enough that you don't have to write a HUGE check.
Many banks will help you in setting up an account for this stuff. Some banks will say you need to have a business license; that's a tricky one because legally, as a model, you don't need a license but, if you want to write-off things from your business (clothing, travel, lodging, etc...) then you kinda need to be a business. That's actually simple and in most cities you can get a small business lic. for $150 and BTW that's renewable (and tax deductable too).
It may seem complicated but, it's really not some things to remember; document everything, keep receipts, and either buy Quicken or Quickbooks (Quicken will do what you'll need) the later is more for businesses that sell stuff.... you.... you're renting your time. You invoice for your work and you get paid toward that invoice; that can be a simple receipt booklet thing if you wanted. If you want to be more polished and professional, have some form thing printed up.
If you have other questions on this look me up on my website: www.lifeimagesproductions.com and email or call me. I've helped many a model on this part of the business. Funny, just did this two days ago for 4 friends. ;-) Good luck to you.