The trick to making perfect looking waffles is to not overload the waffle maker with batter. I have a large serving spoon which I use to portion the batter - just over a spoonful per waffle. It might take you some trial-and-error to get the right quantity for your machine. Just allow some time for cleaning up the overspill afterwards!
Use a whisk to stir together the flour and baking powder.
Crack in the egg and start to mix it in, it doesn't need to be thoroughly combined at this stage.
Add the milk, starting with a small amount to prevent lumps. Whisk together until you have a smooth batter. It will have quite a thin consistency, but if you leave it to rest for 5-10 mins it will thicken up. Conveniently, this is about the amount of time it takes the waffle maker to heat up.
Cook the waffles in batches for 5-6 mins each, using the oil to grease the waffle maker before each waffle. Make sure you use a heatproof brush.