You don't need a lawyer to file for bankruptcy unless you're filing on behalf of a corporation or larger LLC. A lawyer is great for ensuring you get your paperwork completed correctly and use the laws to get the most debt discharged while protecting all of your property, but if you've got a simple chapter 7 and no extraneous assets, you can certainly do it yourself.
What You Will Need
You will first need to get a list of all of your creditors, both secured and unsecured, as well as all of your most recent income records, pay stubs, etc.
You're also going to need your tax records from the previous three years. If you haven't paid your taxes, you're going to have a very hard time and you should definitely call a lawyer.
Go to the Credit Counseling
Before you really begin anything, you'll need to go to an approved credit counseling session. This requirement is part of the 2005 BAPCPA (Bankruptcy Abuse Prevention and Consumer Protection Act) which made the bankruptcy laws a little more complicated and added steps for people wanting to file (This reform was driven by creditors who felt bankruptcy was "too easy" and that people were abusing it).
Here's a list of approved counseling agencies from the Justice Department.
The Process
For a simple chapter 7 case, the process is not terribly difficult, but the paperwork IS long and confusing and contains a lot of legal jargon. There is the bankruptcy petition itself, which is very simple, and then there are about 15 associated "schedules" that primarily outline things like your unsecured debts, priority unsecured debts (student loans, family support debt, IRS debt, etc.), your assets, secured debts like a mortgage, your exempt equity, information on any leases, your real estate holdings and similar financial information.
You can find a lot of information online, but if you really want to file for bankruptcy on your own and do it right, you should pick up a how to book. Nolo's How to File for Chapter 7 Bankruptcy is one of the best books out there. It's written by an experienced bankruptcy attorney in plain English, so anyone can navigate the process.
The Bankruptcy Hearing
Commonly called the 341 meeting of creditors, it's unlikely that any creditors will show up. Really, if you've done all your paperwork correctly, then the hearing should only take a few minutes. The bankruptcy trustee assigned to your case will go over the information that you have provided to ensure that it's accurate and that you are aware of everything in it. Make sure you bring an ID and dress appropriately.
If you're up for doing it yourself, get the Nolo book and read through it BEFORE you do anything else. If you feel that you can handle it, then you can save yourself $1,500 or more by skipping the lawyer. If it turns out that you're not comfortable doing it on your own, then at least you'll be much better prepared when you do meet with a lawyer, and you'll know all the right questions to ask.