It's been a little while since I started playing guitar, but I'm going to make an effort to remember back to my roots. At the same time, I'm going to focus on things that ruin my life to this day as a recording guy.
1)Guitar playing means nothing. Make a list of your favorite songs. Odds are very strong that they are extremely easy to play for anyone who has been playing guitar for more than a few months. There may be one or two parts or maybe a guitar solo that are quite a bit more challenging, but the rock stars who wrote the song are capable of playing just about anything they wanted to. However, they chose to write songs that may not be the most complex on guitar, but sound the best to their ear (and obviously yours as well). There are exceptions to this. Off hand, Jazz and Metal come to mind. Those are different animals altogether. Of course, even the best metal songs in my opinion are generally simple by nature.
If you go into guitar playing trying to compete with Steve Vai or the mega shredders, you are going to make a few discoveries. One, to play like those guys without being totally sloppy is very difficult. Two, very very few people actually care or are even impacted by the shredder community. Basically, don't play guitar for the sake of playing guitar. Play guitar for something bigger...like to serve a great song. That's the reason you started playing guitar in the first place. Almost all guitar players forget that as they get more advanced in their instrument.
2)Timing means everything. I remember reading in a guitar book that told me to tap my foot while I played. To me, this sounded like something that people who played “Mary Had A Little Lamb” would do. I didn't see my rock star influences tapping their foot. Well, the other day I was playing guitar trying to figure out a tempo for a song and what do you know. I was tapping my foot.
In reality, tapping a foot is not near good enough. A metronome is a must for any guitar player who ever intends of doing anything professionally. I don't have time for musicians who can't play in time. It's too much work to fix them. While you will grow into doing more and more complex things on your guitar, you will find that you probably don't have anywhere near the timing chops that the big boys do. Seriously, the big boys may only be playing 3 chords, but they can do it better than anybody. That's why they are paid a lot of money to do so.
There are other options out there. There are a lot of “jam to this” type of deals that let you play along with guitar and bass or whatever. I highly recommend these because they force you to play in time in a fun natural way.
The same applies to playing along to your favorite cds. These cds force you to play at the right tempo with great timing. Most people simply don't do enough of this.
If you want to be a lead player, nothing is more important than a metronome. I didn't practice with a metronome nearly enough. Because of it, I became sloppy. If you really want to be a great player, it's very difficult to do without hours of practice with the click. (same goes for drummers as well).
3)Consistently practice. If you only have 15 minutes per day for guitar, I recommend playing 15 minutes per day. It's better to practice a little bit each day than it is to practice in an hour or 10 one day and then wait a week before you pick up your guitar again. You'll be amazed at home much better you get by simply sticking with it.
4)Have Fun With It. Guitar is supposed to be fun. Do things to make it fun. Whether this means learning new songs on a regular basis or buying a cheap little recording program, go out of your way to make it fun and interesting.
5)Start Writing Songs NOW! I know many damn good electric guitar players that can shred their asses off. They usually work at factories or restaraunts or whatever (nothing wrong with that). However, there are guys who live in mansions just 20 miles from my house that have written a few songs that had enormous success. I guess my point is that there are a lot of guitar players and not a lot of work. Great songwriters will ALWAYS be in demand. If you can write songs, you can play guitar for a living. If you can't write songs, you better stay in school.
Conclusion
There are a million tips I can give you, but timing and songwriting are the only things that matter to me when I'm recording a band or guitar player. On a record, people pretty much only hear songwriting. Well, that's what I say everyone should focus on...especially beginners.