You can never be too obvious. It is always crucial to signal before moving left. Just put your left arm straight out.  Be sure to check your mirror behind you before signaling to avoid injuring your arm by a car passing too closely.

Right turns can be signalled either by pointing the right arm straight out, or with the traditional left arm bent at the elbow and pointing up.

And don't forget the left arm bent and pointing downwards to signal an intent to stop.

Signals are meant to signal intention, which means we do it before beginning an action. This can be tricky for cyclists as we also need to control our bikes, sometimes with two hands as we approach an intersections and need to slow down, especially in wet weather. Be aware that although you may have signaled once, you don't have a continuous signal like a motor vehicle and drivers may have missed it.