Actually, it's a case of "if it ain't broke, don't fix it"...! You say you are already getting "great results". If so, then I'd say adding a preamp isn't likely to help anything, and could possibly impair your signals. The only time a preamp makes sense is in marginal conditions (like mine!) when signal reception is spotty at best, and addition of a preamp makes enough boost in the signal received at the set to improve the chances that I receive a nearly "error-free" signal that the set can resolve to a usable picture and audio a higher percentage of time. Things were a lot easier with analog signals where you could see for yourself if changes you made were improving or hurting the signal. Now in the digital age, it's pretty much all or nothing. You either have a rock solid picture, or you have nothing. In between you may have pixelations and drop-outs, but you are really hard pressed without sophisticated equipment to know whether or not those are due to poor/variable signal strength or multipath interference, or a combination. And the difference is important.
In your case, I would do like navychop mentioned and raise the antenna as high as practical, possibly needing guy wires for support. I'd also use a good quality RG-6/U coax cable from the antenna into the house. But I would not add a preamp unless I have spotty signal strength, leading to the results mentioned above. And then, which one becomes somewhat of a crapshoot unless you know exactly why the signal is spotty. You might do well with a medium gain amp, but one with a very low noise figure, like the Winegard HDP-269. If you need higher gain, the Channel Master CM7777 is a good choice. You might also need high overload protection and/or an FM trap if the signal(s) you're trying to get are distant and being overridden by local channels or FM stations. Noise generated in the preamp is the enemy for a clean digital signal, which is the primary reason I say not to add any preamp unless you know for sure you need one. Even then, get the lowest gain unit that will meet your needs because higher gain always equals higher added noise. DON'T get a preamp from a place like Radio Shack. They're marginal best. BTW - Installing a superior antenna (higher gain in the bands of choice) is a better idea than adding a preamp. Getting any antenna pointed to the best position is also a challenge, and critical. A good rotator helps with that, also as mentioned before.
Here's a good resource to see what stations are available to you, their relative bearings and distance, etc.:
AntennaWeb
My grounding recommendation: an 8' ground rod driven into the soil at the base of the antenna, 8 ga. or (better) 6 ga. solid copper wire attached to the antenna itself (the grounded parts) and the mast via a ground clamp(s), running unbroken to, then attached to that ground rod, and then ultimately running unbroken to the ground at your electrical entrance panel inside your house. All coax cables need to run through a grounding block installed near the point of entry to the house to ground the shield parts of the cables, and those ground blocks are also attached to your ground wire. Check the NEC and local codes for exact requirements in your area. IMPORTANT NOTE: NO economically-viable residential grounding scheme is going to protect you from a direct lightning hit. But it will protect you from static buildup that will affect performance and could damage your equipment, and it will probably protect you from the EMP of a nearby strike. Make sure to also have surge protection for your equipment, and it's still best to remove power and antenna connections during thunder storms! Your homeowner's insurance will also want to know that your system was properly grounded before honoring a claim for lightning damage!
Install your antenna first without a preamp and properly ground it. Try it that way for a while before you decide to add a preamp, then do some research to see what you really need for your situation.
Welcome to the forum and good luck with your project...!
