Going on holiday with friends is one of the best ways to travel. You are able to experience new places (or revisit old ones) with the comfort and companionship of people close to you. The only big stress is trying to get it organized, which is where this guide steps in.

[edit] Steps

The most important thing to decide first is where you want to go. Maybe you have an idea of a place you want to visit but don't know who to go with, or perhaps you and friends decided together that you wanted to go somewhere specific. Either way, the location is what defines the rest of the planning.
Once you have decided on where to go, you must decide who to go with. The reason you decide the place first is because certain people don't do well in certain places. You wouldn't want to take a friend who sunburns easily on a desert hiking trip. If you made the decision with a group of friends on where to go, then make sure you can handle being with those people for however long you are going away. Also think about anyone who might not have been there for the idea but would still love to go.
Length of the trip is the next decision. Work out how many days you can take off and try to think around major holidays so that you can stay longer without missing extra days of work, school, etc. Use those holidays to your advantage, that's why you have them!
Once you know where, with who and for how long the trip is, book it. You can always go through a travel agent if you want to keep things really simple, but of course you will pay a lot more for their time. You can always jump online and find cheap fares easily. Utilize the sites that are meant to save money and time, such as Travelocity, Priceline, Hotwire, Orbitz, Expedia, etc. They are all money-saving sites where you can even package flights, hotels and rental cars. Sometimes they even have special deals for certain places, per number of days and number of people, so always check those specials first.
Last but not least, make sure that you try to plan at least a few things to do once you get to your destination. You don't want to reach there and then argue with your friends about what to see and do in the amount of time. Maybe you can each pick something to do and agree that everyone has to do all of those, and then everything else can be spur of the moment.
Enjoy your trip!

[edit] Tips

If you are a student or youth, a great website to use is (www.isecard.com). You can get a card through them for $25, and use it to get great deals on hostels, flights, trains, etc. all over the world.
Be sure to take a lot of photos. If you don't want to carry an expensive camera, you can buy a cheap disposable digital camera at any major store like Wal-Mart.
Another way to keep all the memories for once the trip is over, is to take a little journal. Nothing big, even just a little notepad you can put in a purse or pocket. This comes in handy especially if you meet great people along the way and want to get their information to keep in touch. As long as you have a journal from the trip, you'll always know where to find the details.

[edit] Warnings

Be sure to include all of the trip members in each decision. You don't want to anger anyone by leaving them out, even if it's as simple as what time of day to leave/return.