For my first dry mix I use regular flour (1 cup) and 1/4 cup corn starch and set aside. The wet mix can be a basic egg wash, egg & cream, butter milk etc... you want something lighter than a batter but thicker than water. The last mix I use 1 cup of flour, 1/2 cup of my hush puppy mix
Choosing a fish is the next part. I don't like fatty fish like tuna and salmon fried. To me it's like the oils collide and it's not pretty on my palate. I like firm white/pink fish. Catfish, cod, halibut, tilapia and flounder are favorites (flounder is on the delicate side so wait until your frying is up to snuff before you go there). Pat your fillets dry before you begin... Now dust in the first dry mix and pat off the extra flour, do two or three and then set them in the wet mix. Flip the fish in the wet mix and then one at a time place a fillet in the dry mix and coat thoroughly. Lightly share off excess flour and place on a plate to rest.
For the oil I like safflower or canola oils as they have a high smoke point and not much flavor. Peanut oil is a good choice but I don't like the taste of peanut oil which I consider a heavy flavor on my light fish. You can use your electric fryer
Since I am using hush puppy mix I do mix a batch of hush puppies for two reasons, I love hush puppies and it's the perfect tester for the oil temperature. Since we are pan frying we want a pan with straight sides, and about 1/4 to 1/2 inch of oil in the pan. When you think the oil is warm enough drop in a bit of hush puppy mix and see if you get vigorous bubbling. If you don't remove the tester and try again in a short while (minute or so). Cook the hush puppies, this too will ensure a good temp for the fish and face it the fish costs more so screw up on the hush puppies. When the first batch is done (nice and brown but not black) remove from the oil and break one open, if the inside is still gooey turn the oil down a bit and try again (the residual heat in the puppies may still cook the interior so check before serving they may still be good).
So the puppies are done (each batch should take about 3 minutes and you will need to flip them as we are pan frying) now it's fish time!!!. Lay two or three fish in the pan laying the fish away from you. Remember that the oil is freeking hot and if it splashes you want it to splash away from you. After about 10 seconds just move a tad with a spatula (silicone)
Now this is a once a month type of thing for us, because none of us really need the extra oil, but doing it properly at home will give you a lighter less oily decadent treat that will far surpass anything you can get at a restaurant. Most restaurants tend to go for an oil temp that is good for fries and ok for fish which I find to be a bit low for the fish. Plus you don't know the condition or the seasoning of the fish which you are now in control of.
For variations, add some herbs to the wet mix here they will give great flavor and will not burn as they are protected by the outer crust.