How is RNAse contamination in RNA based experiments prevented?
You need to be careful about everything that comes in contact with your samples. Every spatula, beaker and every magnetic stir bar need to be RNAse-free. 

For metal- and glassware we usually put everything into a drying closet at 200-250 °C for a few hours. That should get rid of RNAses pretty efficiently.

The RNA chemicals should be seperated from other chemicals if not everyone in the lab is working with RNA. They shouldn't be weighed using spatulas, but just poured into an RNAse-free container to avoid contaminating the storage container.

Use disposable plastic wherever possible, you should be able to perform most stuff in falcons and Eppendorf tubes.

Be careful with performing e.g. a DNA-prep at the same bench as the RNA work. The first buffer for the DNA-prep contains RNAse.

Avoid keeping your Eppendorf tubes or falcons open for long, that should reduce the potential for contamination.

We've had pretty good experience with just using water from a Millipore system and autoclave it once, that seems to get rid of the RNAses. I know that this is not a sure thing as the RNAses can survive autoclaving, but it seems to work well enough.