Oh, the lessons I've learned during my six [now ten] years as a Virtual Assistant...   These are a few commandments:

1. Always trust your instincts - If a client sounds too good to be true, you can bet there are some scary things in his/her closet, stay away!
2. Charge too little and you'll be a doormat
3. Charge too much and you won't land any clients
4. Communication is the #1, most vital element of your business - at a minimum, email back within 24 hours or you're going to lose business.
5. Have a rock solid, non-negotiable work for hire agreement that spells out your and your clients' protections. 

Your Work For Hire Agreement should include:

• A Description of the services you'll provide
• Details regarding payment
• Retainer specifics
• Expenses not included in the contract
• Termination clause
• Details regarding the relationship of parties
• Product ownership
• Confidentiality clause
• Severability clause
• "Entire Agreement" clause
• Jurisdiction clause
• Indemnification clause

One element that I decided to include after a very nasty incident has saved my hide.   Add this to your current agreement ASAP: "The first month’s retainer fee may be held as a cancellation fee" - I had a horrible new client - I hadn't trusted my instincts and I completed at least 12 hours of work for this person - only to discover that she did a "charge back" on her deposit payment and PayPal did NOT protect me - despite my protestations that I had completed the work, I was out over $1000.

If anyone would like a copy of my current Work For Hire Agreement, feel free to send me an email or make a post on the forums and I'll send a copy. [There's now an MS Word and RTF version of my Work for Hire Agreement available for download under the 'Resources' section - go to Documents then Legal and grab your copy!]