One way of telling people what they should do is to use the phrase I think you should…

• I think you should consult a specialist.
• I think you should accept that job.
• I think you should talk to him.

To make a more direct suggestion, you can use You should…

• You should get that car repaired.
• You should find a better job.

To suggest what someone else can do, use the phrase You could…

• You could help him.
• You could ask him to help you.
• ‘What shall I do tomorrow?’ ‘Well, you could go for a long drive.’
• When you’re in London, you could go and see Mary.

If you want to do something, you can say Let’s …

• Let’s go for a walk, shall we?
• Let’s buy something to eat. I’m starved!
• Let’s buy some flowers for her.

If you want to make a suggestion and see if other people agree with you, use Shall we…

• Shall we go for a walk?
• Shall we buy something to eat?
• Shall we ask Susie if she wants to come with us?
• Shall we buy a new home?

Another very common way of making suggestions is to use the phrase How about…?

• How about buying something to eat?
• How about watching a film?
• How about taking a short break?
• How about buying a new car?
• How about asking his help?
• How about going for a drive?

Note that a verb used after How about…? should be in the –ing form.