A common mistake is to use a float that is too light, which makes casting difficult and is very likely to be dragged out of position by the wind or undertow.
Select a float that allows you to easily cast past the spot you are fishing and wind it back into position, sinking the line as you do so by pushing the rod-tip underwater.
A straight peacock or crystal waggler is my float of choice, but I will switch to an insert waggler with a finer tip if bites are finicky.
In terms of size, a float carrying 4AAA is a good starting point in water 6ft-8ft deep and I lock it in place with two movable float stops. I’ll then have an AAA shot at half depth and a BB and several No4s spaced between the AAA and the hook.
I like to present my hookbait slightly overdepth with about 4ins of line laid on the bottom. If there’s a lot of undertow, place a No6 shot just on the bottom. With this set-up the bites are usually very positive, with the float often rising slightly before disappearing under the surface.