Feeding

There are as many opinions as there are fishkeepers 

Assuming you have 'ordinary' community fish, you can feed once or twice a day; if you feed twice use half the amount each time as you would if feeding once a day.
As a very rough guide, a fish's eyeball is about the same size as its eye. In one day you should feed the amount of food equal to one eye per fish in the tank. Which I realise is impossible to work out, but it is an indication that fish need less food than most people think.

A lot of people don't feed anything for one or sometimes two days every week. This is because in the wild fish don't find food every day. I admit that I don't do this, I feed every day.

It is also a good idea to feed more than one type of food. I use flake, small sinking pellets and algae wafers. And there is also live food, though I prefer frozen 'live'. These should be fed no more than once a week as they have less nutritional value than commercially prepared food. The cubes of frozen food contain more than is needed by an average sized tank of fish. I have a special knife to chop the cubes into bits before defrosting and feeding just one piece.

Fruit and veg can also be fed to the fish - I have just posted about that here