I don't consider myself a travel expert but I might have picked up a few things. This year I've had the opportunity to rent cars and travel to several cities in the US and thought I could spew some tips your way.
First off, getting there. "Book early" should be your mantra. In booking airline flights, try to hit the internet on a Tuesday. Monday night is when fares change and other airlines try to match them the next day. Hence, fares are generally at their lowest on Tuesdays. On the flip side, beware of booking during the weekend when everyone and their uncle searches for flights. It's true sometimes you can get a break a month before you depart on a long distance flight, but in my experience, give yourself a good lead time before your trip. I've booked flights as much as 6 months before the trip for best rates. But I've heard people say six weeks prior is the best time to buy. It all depends on how heavy the traffic is at the time of travel. Naturally you can expect holiday flights to fill up quite early. If you only book two weeks before you travel, you will probably end up paying premium as the airlines will think you are a business traveler.
Always do internet comparison searches. At times, I've found Expedia.com to be cheaper than Orbitz.com and vice versa, but other times, CheapTickets.com will blow them all away. So there is no one website consistent in lowest prices, as they know they are all competing against each other. It's all variable. So try a website like Kayak where you can do comparison shopping.
My website of choice for hotels is Hotels.com. This is because if you book 10 nights thru their website, you are rewarded with a free hotel night. And you still pretty much get a good deal on the hotel prices.
When renting cars, I'm fond of CarRentals.com. There are two options they ask when you rent. One is to pre-buy the gas and two, is whether or not you want insurance (extra charge per day) for the car. I usually don't pre-buy the tank of gas. Here's my argument. Sure, pre-purchasing a tank of gas is convenient, especially if you are in a hurry and don't want to waste time looking for a gas station, then that option is for you. However, note that most people don't really wait until the last minute to fill up their tank. I always get nervous about the amount of gas left in the tank in a rental when the meter shows 1/4 full. If you pre-buy a tank and give them back the car when you are 1/4 full, you've just given them that 1/4 tank, plus the extra reserve gallon for when the gaslight goes on. Best bet in terms of cost saving on a rental car is to ask the rental car clerk where the nearest gas station is before you take off with the rental, in order to expedite the time you need to fill-up before you give the car back. This will save you time driving around looking for the closest gas station to get that topper.
And regarding insurance, I always decline getting insurance on a car rental. People don't realize you can use your regular car insurance to cover the rental (or least most policies will cover a rental, check before you drive off). Of course, if you are nervous about driving a rental and don't mind paying the extra ten bucks a day for insurance, go for it. There's nothing like peace of mind.
As I said, I am no expert, so please post any additional travel tips you might want to add. I'll read them all. Thanks!