My advice is pretty much in line with everyone else.
Review items you already own that Lovehoney stock (doesn’t matter if it was purchased elsewhere), make the reviews clear and informative.
Applying for items similar to ones you have already reviewed is probably a better option than something totally different.
There are a few topics on here if you search 
with reviews so you can get a feel for some good ones 
Have patience and remember that being selected to test is a privilege, not a right 
You can also scan through Sex Toy Tester - Chit-Chat for tips.