any tips to write a song?

just write something, anything. just make it. you can clean it up later.

starting with the chorus would be a good idea, and then expanding on those ideas in the verses. this is really nitpicky but be careful with your rhymes, i'd say to avoid really perfect rhymes that'd be almost stereotypical? eg i'll cringe if i see 'kiss' rhymed with 'bliss' but that's just me lol. you can do whatever you want! it's your art.

with writing lyrics, there's no way thats "right" or "wrong" with it. 

how i do it, is a structure with.. 

a 
b
a
b

the A is where you write a short sentence.
the B is another short sentence, but you rhyme at the end to go with section A. 

then repeat that structure for the chorus. then finally, do the same thing for the bridge part.  

Don't force yourself to come up w/ lyrics, let them come naturally and take a break if u can't think of anything