Hey. I've been trying to play guitar seriously over the last few days, after too much time (several years) of seldom playing and basically just noodling around. I'm slowly recovering the guitar chops I had years ago (even though I've never really been good), and I'm trying to practice the correct way for the first time, with a metronome. I never really had done that before.

I will soon introduce exercises like scale picking into my practice schedule but right now, I'm only learning songs, because that's what motivates me the most. So I pick the song apart, I identify which parts are giving me trouble, I isolate them and I play them at a speed slow enough so that I don't make too much mistakes, with the steady beat of the metronome clicking in the background (I'm in a love/hate relationship with this dude, by the way).

Since I've never learned to practice correctly, I would just like to know if this is the right way to do things. It certainly seems to be the most logical way, but sometimes I wonder if it is that efficient. On some days, I'm a bit stressed out by the metronome, and I screw up more often when it's on. But I also need it to keep track of my progress.
On some parts, I need to go down to ridiculously slow speeds. It's like all the songs I'm learning are played by a doom metal band. What's even more frustrating is that I'm having difficulties with only one small passage, like one chord change, in the whole song. I can play everything else almost at normal speed.
Another thing I need to know is when should I speed up? What should be the threshold, the moment where I know I can speed things up a little?
And I guess that if I keep screwing up when I play slow, almost as much as at normal speed, I need to go even slower, right?

I've only been playing seriously for a few days, but I haven't felt a lot of progress as of now. I guess I have to reaccustom myself with the instrument...
I suggest starting with 1 note/strum per click. this is at a speed you can comfortably hit every note correctly without feeling left behind. next take into account rests or notes held for more beats and factor in clicks for those i.e. 2 clicks per rest and 4 clicks for a held note or w.e the song calls for. again SLOWLY! where you are comfortable and can play it 100% correctly. Next slowly increase speed little by little, if you make a mistake its okay to stay at that speed a little longer until you get comfortable and continue on.

ALSO if you can get a body motion in time with the metronome i.e. foot tapping or head nodding etc.

Focus on clean clear notes/strums, the goal is not speed but accuracy. speed is a result of accuracy.
Start at the speed you can comfortably play at without making any mistakes, even if this is incredibly slow. Gradually increase your speed by 4 - 10 BPM once you've learnt to play a section at your current speed.

If there's a particular bar or chord change that's difficult, focus on practising only that section, starting at the speed at which you can play it correctly.