Use your network for find people, search online Upwork is great place, find work you admire then find out who did it.
Short list people you would like to work with and review their work to ensure they are indeed a good fit for your brief.
Get at least three quotes, always. Always ask for two references for each freelancer and call them.
Take time to give a detailed brief and where possible meet in person to talk through the brief together.
Ask for them to come back with a fully costed proposal that is broken down into as much detail as possible.
Don't ask for work for free in advance, but do ask for an accurate quote.
Have a clear contract / working agreement. What happens if work is late? What happens if there is a dispute? How many revisions/edits/bug fixes are included? If on going work is needed what will it be charged at?
Freelancers / contractors may have networks and relationships that can supply or provide services cheaper than you can access on your own!