1. Keep a "wins" journal
- When you get through an exercise at a particular tempo without making a mistake
- When you learn a new chord or a new lick
- When you practiced (at all) that day
- When you like the way your guitar sounds
2. Don't look at the neck
3. Use a metronome
You think you're doing pretty good? Put a metronome or drumbeat on, loop your exercise, and see how consistent you really are. I suspect you will find you are not as fast or consistent as you think.
Metronomes aren't scores. Higher isn't better, slower isn't worse. Metronomes are simply ways of helping you practice better.
Start with the metronome slow enough that you can get through something (your scale or exercise) easily. When you are smooth and fluid, bump up the tempo up a little. Repeat. If you get it so fast you are struggling, back it down until you can get through your piece.
Do not "chase" the metronome or try to keep up. The metronome is telling you where you are, not where you should be. Slow down, get smooth, then you can go a little faster. The metronome will give you some objective feedback about your progress, and it will reinforce consistency of tempo.
You can get an app for your phone, or use a drum machine (real or virtual).
4. Spaced repetition
You aren't going to get better by practicing the same thing for 4 hours once. You will get better by doing spaced repetition.
That means short, frequent, consistent practice sessions, rather than long, infrequent, occasional practice sessions. 20-30 minutes a day, every day, focused on particular exercises, techniques, and pieces will produce results.
Within that 20-30 minutes, don't spend all the time on one thing. Break it up. Do 3 or 4 things for a few minutes each, then repeat a couple of times.
This is proven to be the best way to learn just about anything.
5. Practice is the answer for everything
Whatever the problem is with your guitar playing, the answer is almost always "practice more".
That includes things like "I don't have any ideas for riffs or songs", "I think I need a new guitar or piece of gear", and "I don't like my guitar sound", as well as the usual problems with chords, rhythms, scales, riffs, string skipping, string bends, alternate picking, sweep picking, or playing lead.
Just practice. Pick up your instrument, give yourself 20-30 minutes, and focus.