I recommend using a thermometer, even if you have an electric fryer. You never really know the temperature of your oil unless you can test the temp.
After a while, you get a sense of how things sizzle, how long different things take, etc. Smell and color tell you things, as well. All senses are involved in cooking; that’s what makes it such an interesting, visceral art.
(One thing I’ve never made is pan-fried chicken - the picnic-favorite kind. But I guess it’s the same as everything - trial and testing and experience makes perfect.)
-JT
Oh yes, we had a thermometer, that’s the only way I knew that it was taking so long to get to the correct temp. :)