Best tools/methods for cleaning

Im starting to notice a gradual build up of what looks like a mix of general muck and limescale in the corners of my tank as well as the heater etc and am wondering what people here use to clean areas such as these?
Will just a basic brush or cloth do the trick?
Do I need to take the fish out of the tank while cleaning bits like that or are they okay to stay in?

I find a toothbrush useful for things like this. Cleaning outside the tank is better, do it under a tap. It's just the media in the filter which needs to be cleaned in old tank water, the casing and other hard objects like heaters can be cleaned in tap water.

I agree, I use common household cleaning items, that have never been used around chemicals.

I use toothbrush’s, DIY algae scrapers, sponges, etc.

the fish can stay in, just like with water changes

For things that can't easily be removed from the tank to clean, do the cleaning just before you start a water change so you can suck up the stuff that comes off as part of the water change.