I think I should + (verb)

This structure is used to talk about something that you feel strongly about doing.

• I think I should buy a new laptop
• I think I should consult a doctor.
• I think I should get a better job.
• I think I should start dieting.
• I think I should stop smoking.
• I think I should give it another try.
• I think I should learn English.

I think you should + verb

This structure is used to give advice or instructions.

• I think you should accept that offer.
• I think you should quit that job.
• I think you should apologize to him.
• I think you should give it another try.
• I think you should make another attempt.

By adding I think, in front of you should, you are making the advice/instruction sound more polite.

Compare:

• You should wait for him. (Direct order)
• I think you should wait for him. (Less direct (and hence more polite) expression of opinion)

I think he / she / they should + verb

You can use this structure to express your opinion.

• I think he should quit now.
• I think she should speak up.
• I think she should mend her ways.
• I think they should leave now.
• I think he should stop chasing her.
• I think he should find a better job.

The structure I don’t think I should can be used to talk about things you are not keen on doing.

Compare:

• I think I should make another attempt. (= I’m in favor of making another attempt.)
• I don’t think I should make another attempt. (=I don’t want to make another attempt.)

More examples are given below.

• I don’t think I should accept this job.
• I don’t think I should get another credit card.
• I don’t think I should attend that event.