How do you pick you hourly rate?
A fair formula that i was given years ago is;
Take the annual salary you would be paid if you were an employee, add 30% to it for overhead/profit and divide by 48 (working weeks in a year) to get your weekly rate. Divide by 40hrs to get the hourly rate.
Another one is to take your annual salary, divide by 250 (working days in a year) to get your daily rate and increase that by 30%, billing in daily units.
The above formula can and should be tweaked based on the project, client, your needs etc.