Pes_Laul,
Huge applause to you for taking this on! I highly encourage you on this. I went through the same thing when I started playing in Jazz band during my high school years. Up until that time I had been pretty much a "play by ear" kind of guy. However I soon realized that I needed to get some skill at sight reading if I was going to play in Jazz band. It was also my dream to be a studio musician so I took it seriously for that reason too. Reading is still not my strong suit but I'm much better at it than I used to be. It's a skill that you need to practice a lot to get good at it, so be patient with yourself and start simple, but work on it every day if you can.
Here are some tips that helped me a lot:
1) get a good book on sight reading for the guitar. Guitar is somewhat unique in terms of sight reading. We have challenges that other instruments don't have to deal with such as being able to sound the same note on various places of the guitar neck. (when you're sight reading, half of the task is to figure out which position you should play out of to make it easier on yourself) For this reason, you need to practice reading the guitar in various positions to get aquainted with which keys work best in different areas of the guitar neck. The book that I would reccomend is this:
"Music Reading for Guitar - The Complete Method by David Oakes" This is basically the sight reading course they teach at GIT. All students there have to learn to sight read. If you're thinking of playing guitar as a profession, it will greatly increase your marketability as a musician if you have some sight reading skills - go for it!
2) Sight read something (anything) every day. One of my early guitar instructors made me buy a basic clarinet book and practice sight reading from that as an exercise. He would randomly poit to a spot on the page and make me sight read it. This was great because the I couldn't use my ear to fake it, I had to actually read the notes on the page

3) Learn to read in various positions on the guitar, and get a feel for which keys work better for various positions. For example, some places on the guitar neck work great for flat keys (like F, Bb, Eb) and other places work better for sharp keys (G, D, A, etc). I find that the 5th position of the guitar neck is pretty good for lots of keys, this way you can move up or down a few frets and catch most of the things you will need.
4) Start with simple tunes first and practice looking ahead in the music as you play. If you try to read everything at the instant you need to play it, it makes it much harder to stay with the music. Practice looking ahead slightly to catch the next few notes before you need to play them.
5) Practice reading rhythms separately (even just using a single note to sound out the rhythms), to get familiar with various phrases and how they look on the page. If you find a new phrase that you don't know, go through it slowly and work it out, then try to comitt it to memory so that it doesn't suprise you the next time you come across it.
Finally, never forget to use your ear! Even though you're sight reading always be listening so that you can make your playing sound natural (as if you're not sight reading), that's the main goal.
I hope this helps, -- Jim