First and foremost, get the Official Guide, 11th ed. There's three books, an orange with math and verbal, green with just math and purple with just verbal. They all have real questions from previous GMATs and are made by the same people who made the test so this is essential.
There's lots of recommendations here on the site that you can browse through. Personally, I found the Manhattan Review
books to be really helpful since I took their course too and it was good complimentary material. I'm sure there's other helpful guides out there, but the OG is a must.