Well...start out on the 4+ sets and gradually go up. Find your most favorite theme as well first and then move on finding themes you just like.

Here are my favorites:

⦁ city

⦁ creator (most favorite)

⦁ lego movie 1 and 2 (retired)

⦁ disney (Frozen and Tangled only)

⦁ star wars

⦁ dots

⦁ jurrasic park/world

⦁ ninjago

⦁ minions the rise of gru

⦁ angry birds movie (Retired)

This Is more about ideas what to build, not what theme to buy, i think, if you Like Cars, build cars, spaceships, animals...

What do you like?