Understand your boss’s attitude. This is very important as you will get to know how to handle things like when to complement and when to criticize in a positive manner. If your boss is serious and lacks a sense of humor, complementing him/her all the time might not help, rather it might get counterproductive.
Praise your boss’s role in front of their superiors. If you think that your boss deserves a complement, do not just do it to their face, do it in front of their superiors as well. Complementing your boss in front of their superiors will make a huge difference as everyone likes to be praised and hates being put down in front of others.
Do not limit your complements to work, you can get frank with the boss and give him/her personal complements as well. For instance, your boss’s dress sense may be good enough and you should not go without praising it.
Write an appreciation email. Writing a formal appreciation email to the boss can work wonders for you. If a project initiated by your boss becomes a success, the best way to let him/her know that their workers are happy is to dash off a brief complimentary email. A thank you email is also good as it will make your boss feel comfortable with you and increase your chances of success.
Throw a party and arrange get-togethers from time to time. If your boss has done something amazing recently, let's say a completion of a difficult task, you can arrange a get-together meeting on Saturdays, or even throw an informal party.
Point out your boss’s mistakes privately, not publicly. If you think that your boss is wrong in his/her assessment and if things are not handled right away, the company may face a huge loss, you can write a short note, telling them that you look at the problem from a different angle and could they please review their strategy.
Be mindful that imposing your thoughts (even if they are right technically) may seem like an overkill.