Common acronyms used in informal US English texts:

Btw = by

the way
ikr = I know right?
Lol = laugh out loud = haha
Tbh = to be honest
Omg = oh my god
Ttyl = talk to you later
AFAIK = as far as I know
Fml = f*** my life (you say when something bad happens)

That’s all I can think off the top of my head! Let me know if you’ve seen one that you’d like to know what it means!