Whether it's wallpaper or paint, colours look different depending on the amount you can see and the light in the room. Here's how to pick your shade

•Check colours in the room you're decorating, not in store. A colour card only shows tiny amounts so can be deceptive; if in doubt, choose a couple of shades lighter. Use a sheet of white paper to isolate your colour choice without it being affected by nearby shades.

•Buy three tester pots in related colours and paint at least 60 sq cm onto lining paper. When dry (colours often dry a little darker) tack them up, trying them on different walls to check the effect.

•Play around with colours online. Use our colour planner to try out selections of colours that go together in a virtual room, a bit like painting by numbers.

•If you're picking wallpaper, buy a single roll, and pin or use Blu-Tack to fix lengths to the wall.

•Always buy paints and wallpapers from the same batch. It's better to overestimate, and return unused tins or rolls, than to mix different batches.

So, you've chosen a colour and have decided on paint – but how do you know which finish to go for?

•In general, this is a simple choice: if you want good coverage and great colour go for hard-wearing acrylic, according to the Paint Quality Institute. There are acrylics for walls and woodwork, and because they are water-based they have less of an odour than traditional gloss and are kinder to the environment.