Where to start with learning music theory.

Try "Theory Without Tears" by David Hodge, in the lessons on this very site
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I'd start with learning to read standard notation. You don't need to "sight read" - in fact, you don't even need to be able to translate what you read into guitar playing - but the fact is, all of music theory is based on standard notation, and tablature is not a substitute. Example: C-F# is a different interval than C-Gb. They sound the same, and in tab they're identical... but in theory there's a difference.

Next I'd learn to spell all the major scales. The major scale is the 'yardstick' we use for pretty much everything in music theory: identifying intervals, naming chords, comparing other scales... if you know them cold, you'll save yourself a lot of confusion.

Then it depends on where your curiosity leads you. The circle of fifths is a good thing to know from a practical point of view, because it will help you remember key signatures and deal with modulations. Understanding chord symbols is another good thing to know - when you see C7+(b9) you'll know exactly what it means.

If you're interested in a deep dive into theory, once you have the basics down I'd learn counterpoint next. Although most conservatories teach harmony before counterpoint, I personally think that's backwards from both a historical point of view (polyphonic counterpoint preceded homophonic chord progressions) and a practical one - you'll have a better understanding of the hows & whys of voice leading before tackling cadential 64 chords and the like. Follow that with a good harmony text. And picking up some basic keyboard skills helps too, because the keyboard is simpler than the fretboard for visualizing theory concepts.

I have two books on music theory I like:

Music Theory for Dummies.
Mal Leonard Music Theory supplement to the Hal Leonard Guitar Method book.

I like them both, but the HL book, which I have on my Kindle, comes with audio for ear training.

PS: Notebook, the link to look at/buy your book is dead. Do you have another?

I'd say learning about these things to begin with, in order (or close enough);

Major scale pattern (2 shapes)(so you can play with the scale and experience it for yourself before learning more about it)
Quarter and Eighth notes & Quarter and eighth note rests
Notes of the open strings
A diagram of all 12 notes of music
Learning the notes on 3rd, 5th and 7th frets on the 6th and 5th strings
2nd & 3rd Intervals
Swung and Straight notes
The major scale formula
What a key is & Major keys
Chords of the major scale
Simple Rhythmic Phrasing: Breathing in between playing for space
Tonalities: Difference between major and minor
How to build a major and minor chord
Chord functions
CAGED System

... And then go from there into more advanced topics. The above is a basic foundation, I think, for melody, rhythm, and harmony.

I recommend to all my students this book:

Harmony and theory by Kevin Wyatt

I Really enjoy this book, it makes theory simple, and logical.

I think in terms of being able to improvise and play songs, you will want to learn key signatures and the circle of fifths. Once you understand the keys that you're playing in, things start to make a lot more sense!

This is a website that's run by keyboard player in one of my favorite bands. He has a section on music theory that I think is very solid.

https://keyboardkraze.com/treble-clef/

I think in terms of being able to improvise and play songs, you will want to learn key signatures and the circle of fifths. Once you understand the keys that you're playing in, things start to make a lot more sense!

Please do not edit posts after approval to include Spam links - we can see them. I've removed it from your post.

Just wondering here, what do you consider to be intermediate level at music theory?

Just wondering here, what do you consider to be intermediate level at music theory?

Grades 4 to 6