Also - always always always have a lighting design. Without one you are blind!

Make sure your lights are appropriate to the room or space.

Agree, #1 step is ALWAYS create a lighting plan!

Make sure that the right light is put in tge right room.

For example, a Victorian house might get a classsic chandelier. A modern house will get downlights.

Dimmers should be used pretty much everywhere - they are great at getting just the right mood.

Indoor globes should generally be warm white rather than cool.

Also be very aware of the beam angle of your light - whether you want spotlights vs diffused lights.

A very simple trick that all professional lighting designer use is to point a light at some furniture, art or unusual wall. 

Less is more: never over do lighting. Minimalist lighting is definitely in!

Ensure that dark spots and bad shadows are lit up. This may be obvious but you would be amazed how many room lightings are destroyed by forgetting that little piece of advice.

You can also point lights up (both indoors and outdoors). Can be a very impressive effect. Hotels use it all the time with walls and trees.

If a room is dull and boring, you should think about lighting up one part more than the other.

Very cheap - anbd very effective - is to use a table lamp and a floor lamp in combination.

Introduce a light that contrasts heavily with the room for example a black shaded light in a white room. Looks spectacular.

Ensure that you have lights around every task that is to occur in tbe room.

Spot lights are so very in, both indoors and outdoors.

Combine different types of lights - the effect is very impressove.