I'm just getting started learning guitar, so please feel free to take my answer with a pinch of salt. I've tried learing guitar many times but always end up giving up due to the lack of progress I appeared to be making. My recommendation is to simply stick with it. Yes it will get boring at times, yes you will get irritated, but the only way is to battle through until it starts to 'click'.
For me it was finding the Justin Sandercoe tutorials that convinced me to have another go, his recommendation is to practice a little but often. 4 or 5 15 minute practice sessions a week are far more enjoyable than a single hour session at the end of the week. Honestly it's far less frustrating if you can work out a simple practice routine for yourself. I find 10-15 minutes every day once I get home from work far easier to fit into my life than playing till my fingers bleed at the weekend. :-)
I find it awkward to play with right and left hand from time to time. Could anyone recommend some good posture tutorial?
Justin provides some good posture advice here. :-)
When I am practicing playing with metronome, repetition becomes very boring even after 10 minutes, especially when I am trying to play
slower. Is there a better method to train with it? I've read about
using background melody and I'll give it a try. Should I give a try to
Guitar Pro too? It has a slow-down mode, but I think it distorts the
melody a bit.
Then don't practice for 10 minutes. Again, Justin recommends some 1 minute practice sessions on his site. If you feel up to it, you can do loads of 1 minute sessions in one sitting, but if all you can handle is 1 or 2, then there's nothing wrong with that. This is meant to be fun, right? :-)
When I am using electric guitar, I can't find the proper tuning and I am never happy with its sound. Should I play with current sound
for now, or should I watch some tutorials about basics of tuning? It
would be nice if someone will recommend these.
I personally practice on my Strat unplugged, firstly bacause it would irritate the missus if I cranked my amp up too much, and secondly bacause I don't want to be distracted and spend hours getting the right sound for a 15 minute practice session.
As for tuning your guitar, get a cheap tuner. It's one of the best investments you can get. I've a small clip on tuner that lives on my guitar, it only cont me about £10. I check the tuning every time I pick iup the guitar. As you get more confident you'll learn how to tune by ear, but I always double check with the tuner just in case.
Each time I train I become very irritated by these problems. Thanks
for any advice.
Stick at it, the irritation will disappear as things start to work for you. Rushing isn't going to help you one little bit. You will get better with time, honest. :-)
Best of luck.