The easy way out

Straight hair
After you have washed your hair, apply leave-in hair oils or serums. Avoid applying them closer to the roots as that can make the hair look flat. Hair can become frizzy due to excess humidity and so adding a leave-in helps with combating it.
Rice water is a great way to manage frizz. You can apply it on your hair for 15 to 20 minutes just before shampooing. 
Use products as per the density of your hair. Limp hair needs light weight products whereas thick hair will need slightly heavier products to tame the frizz.