Decide upon your time frame. Alaska is a large state and there are a lot of things to see. Determining the amount of time you would like to spend will help you develop your budget later on.
Visit an official Alaska planner website such as the one at TravelAlaska.com. Using an online planner will really help you get a feel for what you want to experience during your trip.
Develop your budget. After you have an idea of what you want to do and see, look into the costs of each activity. Most of this information is available on travel planner sites. Keep in mind the seasonal price variations.
Book airline tickets, hotels and entrance fees ahead of time. You can often get package deals through a touring agency. This could include airfare, hotels, entrance fees and some meals. If you're looking for a more individualized experience, you can often create your own package through a qualified travel agent.
Consider traveling in the off-season. Real off-season prices show up before Memorial Day and after Labor Day.