If you're a dog walker or pet sitter running your own business, invoicing is probably one of those jobs that sits at the bottom of the to-do list until it can't be ignored any longer. You've spent the month doing the actual work: the walks, the check-ins, the muddy towels. Now you've got to piece together what everyone owes you before you can get paid.

Here's a practical guide to doing it properly, without it eating your Sunday evening.