Tip 1 - FunctionThere are 3 basic types of lighting that every space should incorporate - Ambient, Task and Accent.
Ambient lighting gives off the general lighting in a space. Use ambient lighting buy installing chandeliers, hall way flush mounts and recessed lighting in a kitchen.
Task lighting is used to preform specific tasks and should be free of any distracting glare or shadows. Use task lighting under kitchen cabinets or displaying a desk lamp.
Accent lighting adds drama and is the main mood lighting. Use this lighting to highlight artwork or an accent wall.
Tip 2 - Size
Make sure to buy the right size light fixture. In general, take the width and the length of the room in feet, add those two lengths together and convert to inches. That is the basic size fixture you should purchase for the space.
For example: If your room is 10' x 14' - add 10+14=24. Your light fixture should be around 24 inches in diameter.
Of course there are always exceptions! But this is an easy equation to use.
Tip 3 - How High to Install?
Every fixture should be installed at different heights. Wall sconces normally are installed 60-65" from the floor and 6' apart when possible.
Chandeliers normally are installed 30-34 inches above a table and 6 1/2 - 7' above the floor in an entry way or living room.
Tip 4 - The Right Table Lamp
Of course there are always more rules and guidelines. BUT it's best to think ahead before buying a lamp. A 24-30" lamp works in most living spaces but it depends on how high your side tables are. The easiest way to know the right height is to sit down. The bottom of the shade should not be higher than eye level.
Also think about the color of the shade on your lamp. A fabric or linen shade will give off more of a warm glow, where as a white shade won't.
Tip 5 - Bulb
I actually think choosing the right light bulb is just as important as choosing the right fixture. Every light bulb puts out a certain amount of light. This is also known as lumens (do not confuse lumens with wattage, which is the amount of energy the bulb uses). If you are trying to provide light for a large space, you will want a bulb with a higher amount lumens. If you want your space to feel more intimate, choose a bulb that has less lumens.
I'm not going to get into the DOZENS of different types of light bulbs, especially since most lamps require an incandescent or CFL bulb. Incandescent bulbs are the common bulbs that you find at the store, they give off great color BUT are horrible when it comes to conserving energy.
CFL bulbs are what I use at my home. They are energy efficient and have a longer lifespan. In the past, designers didn't like to use CFL bulbs because they gave off a bright white light. But the technology has improved in the past years. Now you can buy a warm/soft white color bulb that will look the same as an incandescent bulb.