Return explicitly or implicitly?
It depends on your intent. Your code should use idioms to match what its actually trying to do.

void foo(boolean cake) {
    if (!cake)
        return;

    // TODO some work.
}


Indicates that !cake is a precondition and as such is insignificant to what the function is doing. 

void bar(boolean cake) {
    if (cake)
        //TODO some work.
}


Indicates that cake is an important part of what the function is doing.