what do you mean by good technique?

When playing with good technique, you will be playing in a manner that is pure, without the artifacts of unwanted noise. In other words, you’ll be hearing all of the sound you want to hear and none of the things you don't. Good technique is not in any way synonymous with speed, though increased speed is definitely a by-product. The goal is to achieve clarity of tone through effortlessness of motion.To this end there are three elements that I deem to be sorely neglected, and they are quickness, muting and synchronization. I shall now ramble a bit about these three things.

Quickness is not to be confused with speed. You can play half-notes at 60 beats per minute with great quickness. What quickness means is that your fretting hand fingers and your picking hand are executing their respective motions quickly, and without hesitation or muddiness.
This has nothing to do with the frequency of motions, but with the manner in which each individual motion is executed. When your pick passes through the string, it should not be ground forcefully through the string. The motion should be that of your hand falling through the string, propelled by nothing but its own weight. Your wrist should be like rubber, firm and bouncy. Force is totally undesirable, as it leads to bad tone. The correct motion could be compared to flicking something sticky off of your finger. I won’t speculate as to what the sticky substance might be, but you get the idea. Relaxed, and bouncy, using the weight of the hand to propel the pick through the string. The volume will be determined by how tight a grip you have on the pick, and the thickness of the pick itself. If you’re using a thin pick it’s very difficult to get very loud. This can be very useful for fast strumming patterns when you want to keep your volume consistent.

Muting is the art (and I do mean art) of controlling the sounds you don't want to hear. When you strike a string on a guitar, you are setting into motions a whole series of events. The vibration of a string carries through the resonant wooden body of a guitar which is why they sound so good. The problem is that those vibrations passing through the wood cause the other five strings to vibrate sympathetically, thereby making unwanted noise. We combat this through the clever placement of each hand. Touch the tip of your pinky, and trace your finger all the way down past the base, over the palm to about 1/2” before you arrive at your wrist. This part of your palm is generally going to hover above the bridge of your guitar (where the strings connect to the body). When you’re playing on the 6th string, it won’t make contact with anything. When you advance to the 5th string, it will touch down upon the 6th string, thereby muting it. When you’re playing on the 4th string, your hand will lightly cover both the 6th and 5th strings. This continues all the way towards the floor, so that by the time you get to the 1st string, the palm of your picking hand is muting every string except the 1st, which is the only one you want to hear.

While you’re doing all of this with your fretting hand, your fretting hand will be very busy tending to the strings that are closer to the floor. This is done mostly by your first finger, but the others will have to join in at times too. It’s sort of the inverse of what was described in the previous paragraph. When you’re playing on the 1st string, all of the necessary muting will be done with your picking hand, when you’re playing notes on the second string that 1st string is going to be able to make all the racket in the world and there’s not a thing your picking had can do about it. The idea is to rest the padded area of the index finger of your fretting hand (about halfway between the tip and the first knuckle) lightly over the 1st string. With attention and practice you’ll be able to do this without interfering with that finger’s ability to play notes. This concept will also be stretched out over the surface of the fingerboard, so that when you’re playing notes on the 6th string your entire index finger is making gentle contact with all of the other strings on your guitar, rendering them silent.

Boiled down, the idea is that any string fatter than the one you’re playing is muted with your picking hand, while any string skinnier that the one you’re playing is taken care of with your fretting hand. To say that this takes practice and patience is a massive understatement, but it will become natural with time.

Synchronization means that your picking hand and the fingers of your fretting hand are operating together in such a way that the pick strikes the string at the exact instant you finger hits the fret. This sounds obvious, but it is probably the number one element in why you can hear two different guitarists play the same thing, both reasonably well, but one of them just seems a bit off. Poor synchronization results in all kinds of artifacts. If your pick hits the string before your finger falls on the fret, you’re going to hear two different sounds where you should hear one. If your fretting fingers are early you’re going to hear the same note twice, once from the pressure of your finger hitting the string, and again when the pick hits. Even if it’s a quarter of a second
it matters, big time, and everybody will perceive that you’re not as clean as you could be, even though they have no idea why.

Finger Exercise is perhaps your best defense against this. Start it off, and make sure that as each finger falls down the pick is perfectly in sync. A metronome will provide great assistance with this, as it provides a target for both hands to “shoot at”. Take it all the way to the 1st string, 4th fret, also paying attention to what was discussed in the above paragraphs, namely quickness and muting. When you turn around to go in the opposite direction things get a little more interesting, because you have to synchronize three motions, because you’ve got one finger coming up, one going down and your pick passing through the string simultaneously. If you lift a finger up too soon, you’re going to get very choppy results. You want each not to ring out until the very instant the next one begins. This will create a very desired legato (smooth) sound in your playing that your audience will be very thankful for.

I’ll say it again; these ideas, like many of the others on this site are going to take real work and commitment to cultivate. Be patient, and know that if you put all of these ideas to work in your playing, you’ll be that player who everybody thinks sounds better than the other guy, but nobody is really sure why, and that is a really fun place to be.