Picking up on Buster's first post:
Some CB's have the SWR meter built in. Or, you may be able to find a used meter at a garage sale for a quarter or a buck.
The basic meters are pretty simple. There is a forward/reverse switch. Set the switch to forward, press the mike button, and set the sensitivty or calibration knob so the meter reads 100% of the radio's power (full scale).
Flip the switch to reverse, and if it reads zero (100% of the power goes out into the air) you are golden. That can happen with business band, but it's not as likely to happen on any given channel with CB.
If it reads 2:1 (90% power into the air, 10% back), tube type sets (remember those?) are completely happy, and most transistor sets won't complain unless they've been modified to the razor's edge of extreme illegal performance. Most sets won't complain about 3:1 either. And receiving isn't fussy at all, just transmitting, though a well-tuned antenna will hear just a litltle bit better.
If the meter reads 1.5:1 on reflected power (96% power into the air, 4% back) or less, just about everything ever made will be very happy.
Tuning the antenna:
Lower channels (Channel 1) need a slightly longer whip than higher channels (Channel 40). If the reflected power is lowest in the center channels, and goes up a little bit at both extremes, but not over 2:1, you are good to go. If it dips in the middle but is a bit too high everywhere, look for something like a bad antenna ground (insulated by rust or paint).
Also, look for metal close to the antennas, especially within a few inches of any loading coils. Since the frequency is so low, metal within 10-15 feet around an antenna may have some affect on the tuning. I've had DOT trucks with cab-top antennas give different readings with the doors open and the doors closed! And check the tuning outdoors, not in a garage with metal ceiling supports.
If both forward and reflected are full scale, look for a bad cable or shorted or broken connector.
If the reflected power is a little high, but lower on the highest channels, you might be able to lengthen the whips or tip tuning screws a little bit to try and bring down the center of the tuning.
If the reflected power is least on the lowest channels and very high at the highest, the whip is long and might be able to be shortened a bit. A brand new tunable antenna might have a whip cutting chart, but it is usually only accurate for a roof mount, or other mount clear of metal obstructions. If using a chart, I start 10% longer and trim from there.
Some metal whips can be removed by loosening a set screw, and cut shorter at the bottom. A grinding wheel is the easiest way to cut stainless steel. I usually cut no more than 1/4 inch at a time, and measure twice. Measure the high, low, and middle channels after each cut. Once a cut gives no more improvement, STOP!
If you suspect an SWR meter is inaccurate, turn it around! Connect the antenna to the radio end, the radio to the antenna end. Calibrate transmit power on reverse instead of forward, and read the antenna tuning on forward instead of reverse. A good SWR meter will give the same results regardless of whether it's used backwards or forwards. If the readings are more than 5% of full scale different, and your meter cable is good, throw the meter away, or have it repaired.
Of course, you can't turn around a meter that's built into the CB set!
Also, a good antenna is more important than more transmit power. It takes roughly 10 times the power to talk twice as far, but you don't hear any better. Four watts feeding an antenna that loses only 3 db compared to a full 9 foot whip antenna will talk 20% farther than a ten-watt radio into an antenna that loses 10 db, and it will hear 20% farther, too. There's a saying among the knowing that $10 spent on a better antenna will get you as much performance as $100 spent on an amplifier.