I think these are some useful tips and things to keep in mind before you plan your trip.
1. Sign up for every airline, car rental, and hotel loyalty card
This may sound like overkill, but all of these entities give deals to their members. Even if you don't have elite status, being a member opens up more opportunities. I have a drawer full of membership cards and most of them never expire. Also, if I ever need to book anything, I have a login and account for just about every company.
2. Sign up for email lists and "like" facebook pages
This may sound like overkill too, but there are so many freebies and extra points or miles to be gained by doing this. You can always unsubscribe from them or create a filter for your inbox. I would say that I don't read most of the emails I get, but I dump them into email folders such as: Las Vegas, Rental Cars, Coupons, Airlines, Reservations, Hotels, etc. in case I need to look for a deal. Again, these companies like to reward loyalty, so you are more likely to find a deal this way.
3. Pick an airline alliance for your loyalty
There are three main airline alliances: Star Alliance, which is the most comprehensive worldwide alliance that includes two domestic airlines - United/Continental Airlines and US Airways; Skyteam alliance, which includes Delta Air Lines, and One World alliance, which includes American Airlines. Look up the various alliances and determine which one would best fit your travel needs. One of the huge benefits for sticking with alliances is the mile/point earning potential. Flying on partner airlines lets you earn on your main airline. Another huge benefit is the redemption of miles. As an example, I used Delta miles to fly on one itinerary on Delta, China Southern, and China Airlines. And you don't have to worry about your bags along the way, as they will be tagged all the way through.
4. Pick a hotel chain for your loyalty
This the equivalent of #3 for hotels. It really depends on the places you travel, but it is relatively easy to always stay within a hotel chain for all traveling. Sometimes it gets old staying with the same chain or chains, but it's worth it because of the perks that may include upgrades, free breakfast, free internet, etc.
5. Get a credit card that contributes to your air/hotel preferences
Every credit card out there has cards that are specifically for a particular hotel chain or airline. Choose one that earns you points/miles on the chains and alliances from #3 and #4. You are beginning to get the point. You start funneling all of your points in the same direction and before you know it, you'll have enough to redeem for your flights or hotel nights.
6. Follow websites
There are a ton of them out there, but follow ones that track deals like: Dan's Deals, Slickdeals, fatwallet, etc. I also follow flyertalk and airliners.net, which are fairly specialized online communities. You might also sign-up to follow: groupon, jetsetter, sniqueaway, or vacationist.
7. Read review sites
There are a million of these too, but I find that tripadvisor is one of the best. I regularly contribute to it too. They have great information and forums in which to participate or read. Virtualtourist and wikitravel are some others. As with everything online you need to sort through some of the crap and determine the validity on your own. Don't get turned off by a single bad review and read through many of them. Many people only write bad reviews/complaints because they are emotionally charged and easier to write.
8. Keep searching even after you book hotel or cars.
If you have ever purchased an airline ticket, you know how much prices can fluctuate. Hotel and rental car prices do too, but not as much as airline tickets. The nice thing about car rentals is that you rarely have to prepay, so you can change the reservation up until the day of the rental. Hotels are a little less flexible and it's best to read the terms and conditions of canceling a reservation. I wait until the very latest to book non-refundable hotel reservations when I am absolutely sure that I will be using it. I usually book a regular rate as soon as I know I need a room to secure a reservation, then periodically search the same hotel to see if rates drop.
9. If you find an airfare deal that suits your needs, book it.
Since airfare fluctuates so much, when you see an amazing deal and the times and dates suit you, then book it. It may not be there the next time you return to it and you will be pissed that you didn't book when you saw it. This is my philosophy at Costco too. I can't count the number of times I've found amazing airfare only to have it gone because I wasn't sure it would work or I needed to check things out. Don't start seriously looking for airfare without a plan in mind. The way I avoid this is to make a list of 3 to 5 different flight scenarios, alternate airports, routings, dates, and times. That way I have some options to work with whenever I look and can book when I see a good deal. Also, run these options by your travel companions to make sure that everyone is on the same page and can live with any of the options.
10. Read up on culture and etiquette.
This is especially important in Asian countries and the Middle East where things that seem like they would be perfectly fine at home would be taken as very rude in other countries. But it's always a good idea to find out about local customs and ways of doing things in that country. I find that books are useful for this. Lonely Planet books always have great sections in their books on this issue.