1- The more you teach yourself, the faster you will progress. If you just memorize what the teacher tells you, without asking yourself ”does this make sense” or “how would I explain this to a beginner”, you will miss a lot. Don’t assume the teacher is always right or that he knows the simplest way to explain things.
Private Lessons or self-taught, the players that get good, fast, are the ones that put the time and effort into it. You can’t stop for a few days and expect to keep up your momentum. Remember, you can practice mapping your fingerboard or running scales(in your head) while you are waiting in a checkout line, or anytime you’re bored. It all counts towards how much time you put into it.
2- If you learn everything (chords, scales, chord progressions) on one string first, it will make much more sense on the grid of the fingerboard. Starting with the key of A makes more sense than E. If the first key you learn is C, you are learning to play the Piano(Piano method, converted to Guitar)
3- All Scales are easier to remember, with their corresponding Chord. You can group this information together. eg. 5th position A Maj scale, is related to a 5th position A Maj chord. You should be able to visualize the Root, Third and Fifth degrees of the scale as a Chord.
4- Learning problem solving, visualization, self-assesment and communication are the most important skills you will gain from playing Guitar. Being fun at parties is just a bonus.
5- The spaces between the notes(numbered intervals I-VII) are more important than the notes themselves. You will be able to transpose and write charts more easily with numbers. Lettered notes have no quantity, unless you already understand music theory, it’s hard to see how an E relates to an A. Most professional/studio musicians use a system call “Nashville Numbering” which is based on Intervals.
Trying to visualize the difference between a Maj and min scale/chord or seeing the relationships that are presented to you in the circle of Fourths and Fifths becomes much easier using numbers.
6- Guitar technique and Musical theory are two separate subjects. Don’t let one, slow down your progress on the other.
7- Learning simple triad chords before the CAGED chords, (and the formula to build them) makes more sense.
8- You can learn just as much from a Drummer or Bassist, as from another Guitarist. Even if they play a completely different style of music than you. A Drummer will have a different approach to playing Music, they will count bars and measures automatically. I find that good Bass players have to understand Harmony.
9- Learning to play the Guitar is not like a pyramid, where you take lessons, pay your dues(bottom level), graduate to being a pro(middle) and eventually are the best(top/pinnacle). The learning pyramid actually upside down, the longer you play and the better you become, the more you are capable of learning. It is impossible to be the best at every style and discipline of Guitar playing. There are a few that come close but for the majority of us, there will ALWAYS be something new to learn! There is always someone that can (technically) play better than you. It’s not a competition, the “BEST” Guitarist is the one that plays the “most like the most like themselves”. Develop your own style.
10- Practicing without the Guitar, being able to visualize notes, scales and chords without any kind of reference is as important as physically playing the Guitar. When you close your eyes, your brain doesn’t know whether the Guitar you are playing is real or imaginary. You don’t need the Guitar to practice!
Edit; Here’s some more points I should really mention. -always be in the habit of tapping your foot and counting.
-Try humming or singing scales, melodies and chord progressions. hearing the sound IN your head is different than hearing your Guitars sound through your ears.
-Warming up(and down) makes a big difference. Guitarists put an incredible strain on their hands. Warming up will keep your hands from cramping, when you have to practice or perform for several hours straight. Learn where your pressure points are, for your hands,arms and shoulders. Here’s a hand reflexology chart . Drink plenty of water.
-This sounds dumb but, breathe. Beginners will hold their breath when concentrating on a particularly challenging piece. I’ve seen lots of people drool on their fingerboards, it happens. You have to be relaxed to perform, trying really hard has an negative effect.
-It’s natural to look down at the fingerboard when you are learning a new piece. If you are playing a song you already know, you should not be able to see the front of the fingerboard when you are playing. This is what I see when I look down at my neck. 
As you can see, I can only see one string, the other 5 are hidden behind it. If you can see the front of the fingerboard, your head and neck are too far forward and the position of your hand is compromised! Don’t tilt the Guitar towards you so you can see the fingerboard.
-A reader reminded me, practice new riffs, scales and chord progressions slowly and build up speed. You will actually be able to play the piece at full speed, sooner if you start slowly. Playing Guitar is a physical performance like dancing or martial arts. The point of practicing slowly is to eventually be able to make perfect, consistent movements, automatically. This is sometimes called “Muscle memory”. Could you tie your shoe the first time you tried? Probably not. Now you do it without thinking.
There are generally 2 types of players, overly studious players that only play what’s on the sheet music, in front of them and self taught players that improvise everything. Try to balance the “book smarts” with “playing by feel”. Being a “Guitar Player” and being a “Musician” are not the same thing, you can be both.
