Check for any weight restrictions by calling your airline or visiting the website. Plan what you are going to wear each day, bearing in mind the nature of your trip. It's also a good idea to check the weather forecast for your destination, so you know whether you will really need those bulky sweaters. Choose a suitcase that is roomy, but lightweight and plan to take some "one-way" clothes that you can discard at you destination if you are going shopping when you get there.
Lay out everything you want to take on the bed. Be ruthless and eliminate anything you are unlikely to wear. Put toiletries, or anything that is likely to leak, into cellophane bags. Consider whether you really need to take items like shampoo. It is often just as easy to buy some when you get to your destination.
Put essential items at the bottom of your suitcase. Stick to one or two main colors for your clothing so you can easily mix and match. Only take about half of what you originally want to take. Take two pairs of shoes--one comfortable pair and a pair for evening. Plan to do a small amount of washing when you get there and take an inflatable hanger, so you can hang a few items to dry.
Roll items like t-shirts. Put socks and small items into shoes. Put easily wrinkled items at the bottom of the case. Ensure medicines and a book to read are kept in your hand luggage. Check the airline website to make sure you have followed security guidelines on luggage. Keep valuables out of your suitcase. Try to keep a light change of clothes in your hand luggage, in case your suitcase is lost.