INT D: Making Suggestions/Giving Advice

 STRONG:
-imperative (command)
-you must
-you have to
-you need to
-you'd better

MILD:
-I suggest/recommend + you + base form
-I suggest/recommend + gerund
-you should/ought to
-you could
-If I were you, I'd... (2nd Conditional)
-If I were in your shoes, I'd  (2nd Conditional)
-Why don't you...
-How about...
-Have you thought about...

To make your suggestions "softer", begin with...
-I think/ I don't think...
-Maybe...
-Perhaps...
-I feel...
-In my opinion...

http://www.ecenglish.com/learnenglish/lessons/giving-advice
http://www.myenglishpages.com/site_php_files/communication-lesson-advice.php
http://esl.about.com/od/grammarstructures/a/f_advice.htm