Curtains serve many purposes in the house. They help control the amount of light coming in. They help create an ambiance, based on the color you choose and the fabric you use. Light colored curtains can make a small room look bigger and more spacious, while dark ones can make you feel warm and cozy even in a big room. You are going to spend different times of the day doing all sorts of activities in different rooms of the house. Hence, the points to keep in mind while doing curtains of each of the rooms would be different.
Two Main Considerations
The amount of light streaming into a room should be your top-most consideration while buying curtains for that room. A brightly lit window means your curtains are going to be subject to direct sunlight for quite some time of the day. Hence the fabric cannot be too delicate, or else it would be worn out because of the sun. The fabric has to stand the heat. If the window in question is rather brightly lit, you would also have to choose a fabric that is thick and in a dark color. At the same time, the color of the curtain should not be so dark that it will fade because of the strong light streaming in through the window. If your window has bars, they would create a pattern on your curtain as the color fades! Now a dark color does not mean one that will totally block the light out (unless, of course, you prefer it that way). Go for a color that will still allow some light to stream in.
The size matters because sometimes certain curtain patterns or colors may not look good on too big or too small windows. A huge floor-to-ceiling french window does not look good adorned with a lace curtain. Though this is only a personal opinion. If the french window is located in a room in the house where too much of direct sunlight does not reach, lace curtains could in fact add the surprise factor to your room and make it appear more interesting and unique. At the same time, a small bay window calls for light colored, light-weight, floating curtains rather than heavy and heavy-colored drapes. The size of your window will also determine the cost of the curtain! This may be quite an important factor if you are going in for an expensive material. However, if you are willing to splurge, this is hardly a matter of concern.
The living room should have a cheerful and welcoming feel to it. It should be airy, and should have enough light streaming in through the windows to NOT let it look gloomy or dull even on a rainy day. This is for the simple reason that you are going to spend quite some time in the living room, and you do not want to be in a place that makes you feel low while watching a sad movie, for example - you would be ultra depressed by the end! Also the living room is where you are going to welcome your guests into. Hence it should feel right. Spend a little extra time and thought on picking curtains and drapes for your living room. If you have a big french window in the living room (thou I envy the most!), it would be a good idea to use layered curtains. You can have a tri-layered curtain - the outer most layer (right next to the window) can be of a simple plain light colored cloth, the middle one can be a lace curtain, and the inner one can be a thick drape. That way you are prepared for every season!
The bedroom curtains have to be chosen with great care. They should create an ambiance conducive to sleeping. Avoid using too dark a color while making curtains for your bedroom. They will make you feel closed in and a tad claustrophobic. If instead, you like the cozy and warm ambiance that dark-colored curtain create, go ahead! However, make sure you use the brighter shades of colors rather than the dull ones. If you are going to use lace curtains, make sure you get them on the window that does NOT invade on your privacy - you do not want any peeping Toms! If you have a bay window in your bedroom, it would be the perfect place to have lace curtains fit.
Go graphic! Tom and Jerry, Duck Tales, Looney Tunes, Cinderella, Pinocchio, Snow White - get them all on the curtains! This is a much better and convenient alternative to getting the walls in your kids' rooms painted with cartoon curtain. Why? Well, your kid is going to grow up and out of the "I love Barbie" and "I want Batman" phase someday, isn't it? Imagine having to re-do the entire room when that happens...! If the cartoons are on the curtains - or even the bed spreads, for that matter - they are going to be a lot easier to change. Also go for durable materials. Avoid delicate curtains. Kids are going to play, throw things around; every play toy that hits the curtain should only hit the curtain and not take a blow at your heart!
The kitchen is a place where you do not want anything coming in your way as you go about preparing breakfast and packing lunch for everybody in the morning. Make sure you select the right material while making drapes in the kitchen. I would personally suggest you go for blinds rather than curtains in the kitchen. They are easy to clean, and will not stain if you or the kids drop anything or spill anything onto them accidentally. The kitchen is also a place where there is going to be fire. Blinds are a much better option when you consider this. A kitchen curtain catching fire is the last thing you want!
Sometimes you might want to segregate a part of the room from the rest of your room. Like you may want to have a dedicated reading corner or a mini-library in the living room, or you may want to have a separate sanctum as your study in the bedroom. Beady curtains are the answer to this question! They look charming and add an interesting element to the room. They can make too structured a room look a little casual. They also help you create a divide without seeming rude or impolite. Beaded curtains can look nice in doorways too, and can serve the purpose of a door or a segregation in a room. Think about it!
Some General Pointers
The Material - Cotton, synthetic fiber, velvet, lace, oh my God! There is SO much to choose from! Think cost, durability, design, fall and texture while choosing the material for your curtains. Let it not be something that will catch too much dust, neither something that will blow and touch the ceiling as soon as you open the window!
Theme-based Curtains - If you have decorated your room keeping a theme in mind (for example, tints and shades of green; or warm colors, etc.) make sure you pick curtains that go with this general theme. If however, you fail to find such curtains, you can simply opt for white, off-white or cream colored curtains - they usually blend in with any kind of colors.
The drapes you use to decorate and embellish the rooms of your house can dramatically change the look and feel of the room - use this to your advantage while selecting curtains, rather than falling prey to a failed choice with respect to this very fact. Do not hurry or rush into a choice. Even if you really like something in an instant, the very moment you set eyes upon it, take the time to look at all your options - you might just find something better. I guess with that, you are fairly sorted and ready to go shopping! All the best!