If you're looking to start freelancing - keep in mind that you'll need some money in reserve as it can take quite a bit longer to be paid (i.e. if you do a month's work and bill at the end of it, you can't rely on them immediately paying that invoice).

From my experience, invoices that say "Payment due within 14 days" have a greater chance of being paid quickly than invoices that said "Payment due on receipt".

Also, the general rule of thumb is - if you're not sure you're charging the right amount, you're almost certainly undercharging.