BB creams are some of the most convenient bases in the history of forever to use. They're much like liquid foundations but with added benefits of hydration, sun protection, and skincare properties. This type of makeup is generally fuss-free to apply, but if you want to maximize them, I just have a few suggestions!
Apply sunscreen beforehand to get the right amount of sun protection and to create a smooth base for your BB cream. Just because your BB cream has SPF so-and-so, it doesn't mean that you'll get that exact number. You will need to apply a whole teaspoon of makeup all over your face to get that promised SPF - but who does that? Realistically you would only use a third of a teaspoon lest your face looks like unbaked cake. You'd still get some sun protection, but it's considerably less than what's noted on the bottle.
CC creams are excellent sunscreens because they're so sheer! Or you can use an ultra light sunblock like the one from Kiehl's
If your BB cream has SPF 50 then you can skip the sunscreen. But at SPF30 you won't be getting much, so just apply your usual skincare with SPF.
To maintain your protection from the harmful rays of the sun, either retouch your BB cream with a powder containing SPF every three hours, or re-apply the BB cream. The former is more convenient. :)
Smooth the BB cream equally all over your face using your hands. Personally I like the smear the BB cream in neat lines, to make sure that I am distributing the product evenly.