modal verbs of advice

stronger

• had (‘d) better + base form 
• had ('d) better + not + base form

use

to express a strong suggestion

• it's very cold! you'd better put your coat on.
• example: you had better finish your assignment before the deadline.

weaker

• ought to + base form
• ought + not + to + base form (very formal)

use

for advice and suggestions

• you ought to take an aspirin.
• example: you ought to try the new restaurant downtown.

for opinions about legal questions or obligations

• you ought to enrol the new course by the end of the week
• example: you ought to comply with the company's policies.

weaker

• should + base form
• shouldn't (should not) + base form 
• should + subject + base form?

use

to give / ask for advice

• you shouldn't speak like your sister!
• example: should i call and reschedule the meeting?

to express a moral obligation, suggestion or personal opinion 

• i should do my homework this afternoon.
• example: i should exercise more regularly for better health.

other expressions for giving advice

if i were you ...

• to say what you would do in the same situation as the other person - example: if i were you, i would apologize to mend things.

imperative

• to give friendly informal advice - example: just go for it! you'll never know until you try.

how about + -ing form? & why don't you ...?

• to make a suggestion - example: how about we meet for coffee tomorrow?