While the Rules of the Road say that your maneuvers should be obvious, let’s talk about why.
When we drive down the road, there is pavement, the pavement has markings, corners often have lights, or stop signs, etc. We all have many hours behind the wheel, and we have learned what to do, what others are likely to do, and act accordingly. But for a moment, imagine that you are out on the Bonneville Salt Flats in Utah. Now you are driving where there is no defined pavement, no pavement markings, no traffic lights or traffic control of any sort, and you see a car coming towards you in the distance. Now what do you do? You have no idea what the other person is going to do. Suddenly all of your years of driving experience are all but worthless. Do you want to make a very slight change of direction to just narrowly miss the other car, or do you want to make darned sure that you do not come close at all?
Now let’s jump into our boat out on the open water, and off in the distance a boat is coming towards you. Perhaps you are the Stand On vessel, now you have to hope the other boater a) knows the Rules of the Road, and b) will comply with them. If you are the Give Way vessel, should you make a tiny course change to just barely miss the other boat, and assume that he can read your mind because he does not know if you a) know the Rules of the Road, and b) will comply with them. This is why the Rules and good seamanship tell you to take obvious action, and why it is important. An exaggerated or major change of course if you are the Give Way vessel says to the other boat: a) I know the Rules of the Road, and b) I am complying. It says it loud and clear.
Oh, and don’t wait until the last minute, do it early to avoid any confusion.