Hello there(finally, been waiting to post this)! 

I wanna try some Thai lakorns or movies(what do they call this in Thai?) but I don't know what to watch and where to watch. Help me please?

Basically here are some genres I am fond of: 

  • school life
  • adventure
  • fantasy
  • comedy
  • horror-comedy(please no pure horror, I watch mainly at night... and alone)
  • investigation
  • law
  • revenge
  • light drama

I don't think I'll like the drama/movie if it was too focused on romance and love. However if you think that romance-centered drama/movie is very much worth it, then recommend away~

Oh, where do you guys watch Thai movies/dramas? Or download?

The genres you mentioned are almost never up in Thai lakorns. They're always centred on romance so there's no escape. Unless they're films.
For starters, you need to not pick any slap/kiss lakorn. They're usually revenge oriented but they're not what you used to see in other revenge dramas. In other words, they contain rape so stay away from them if you don't want to be repulsed.

Let's see, you can start with Pin Anong. It has a bit of everything romance, drama, revenge and even comedy. You can find in YouTube.
Thanks for the recommendation! That'll definitely be my first Thai lakorn

By romance, I meant something like a wife/husband having an affair with someone, then his/her partner found out and then there goes the hair of both women falling on the ground. XD I'm okay with normal romance, especially those couples with good chemistry. Oh is there a medical drama in Thai lakorns?
No there aren't. There are lakorns where the main leads are doctors but they don't actually focus on medical issues. Only his love story and life :D
I agree with Cheer, there's really not a whole lot of genres to choose from. Lakorns also tend to be low-budget, but sometimes it really adds charm to a show when it's light comedy ^^ You can find Lakorn streaming sites on this Tumblr, by the way

And If you do want some fun rom-coms or school life dramas after all, then I suggest dramas like Hormones/Lovesick and Full House, and movies like Hello Stranger, and Suckseed.

Your best bet is to search for Thai movies on MDL and filter based on genre so you'll find movies like Shutter and Pee Mak + lots of horror movies that are in HD and much easier to find online.