I'm new to the CB world and just finished installing my setup, and thought I'd share some things I learned that weren't immediately apparent from reading around as a newbie.
First: Checking SWR is a must. The FAQ here says "You should have your antenna checked and tuned before transmitting", and IMO "should" is an understatement, or at least it was for me. I ran my radio for a few weeks before acquiring an SWR meter, but waited to transmit. Turns out I had an SWR of 3.0. Good thing I never transmitted.
Second: The antenna's location on your car (or at least mine, a standard 4-door sedan) can greatly affect SWR. From the guides I read I had the impression that you just use SWR to tweak the length of your antenna. But it turns out my SWR was so high at 3.0 solely because of location. I have a magnet mounted Little Wil that I placed on my trunk near the side. Since my FM antenna had broken off years ago, I thought that would be a good spot to put my antenna. Aesthetically it was a perfect spot as it looked very natural and hardly stood out. But I believe too much energy was being reflected by the main cabin of my car (I think that's why my SWR was bad). As soon as I moved it to the roof, my SWR got cut to 1.5. This also greatly cut down on my receiving noise and increased range.
Once I put it on the roof, I found that moving my antenna mere inches was changing the SWR by as much as 0.3 up or down. After a lot of guess and check, I found the best spot to be all the way at the back of my roof against the rear windshield trim, and almost all the way to the right side. I found that the closer I moved it to either side, the lower the SWR. I believe this is because the antenna has a completely unobstructed view on one side with none of my car in the way. This got my SWR down to 1.0-1.1.
Third: One of the harder parts for me was figuring out how to get the cable from the outside of my car to inside the cabin, as all guides I could find jumped over this part and I didn't have a whole lot of body work experience with my car and had no idea where to start. So here's what I did in case anyone is looking for ideas: First, I ran the cable into my trunk by running it under the forward lip of my trunk. The rubber seal is soft enough to let the cable comfortably through while the trunk is closed. Next, I did some poking around the top inside of my trunk until I found a hole which ran up under the felt around my center brake light inside my rear windshield. I pulled back the felt around the light and could feed my cable through.
Hope this can help someone!