Hey & welcome!

Originally Posted by: KillboyPowerhead

i'm struggling with triads in improvisation

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Using triads in melody playing, soloing, lead guitar, improvisation is essentially targeting chord tones in the key or scale you are playing in. In order to know which triad to use & where to play it you really need to know your notes all over the fretboard. Not necessarily all the notes of a triad. But if you are playing over an A major chord, for example, you need to know automatically where all the available A notes are. Without having to stop & think about it! So, when you say this.

Originally Posted by: KillboyPowerhead

3) I don't know by heart every note on the guitar neck: for the first 3 strings i do quite well (because of E shape, A shape and D shape bar chord), while the other 3 it requires me a few seconds (sometimes a lot of seconds ;-) ) to understand what notes i'm playing.

[/quote]

I encourage you to spend time learning the notes all over the fretboard. It's not as hard as it seems. Since you already know some of them, just look for the octaves! :)

Having said that, here are some tutorials that might help you. This first one is Dave covering all the basic triads shapes & how to use them in lead playing.

https://www.guitartricks.com/tutorial.php?input=1946

In this tutorial, I show how to find triads & their inversions across the fretboard.

[br]Major triads on the E, B & G strings.

https://www.guitartricks.com/tutorial.php?input=734

Minor traids on the E, B & G strings.[br]https://www.guitartricks.com/tutorial.php?input=2214

To address your other concerns.

Originally Posted by: KillboyPowerhead

1) The same triad note can have 3 shapes (inversions) on each string triplet and i don't know when to use one instead of another given a certain song key.

That's a matter of knowing which voicing you want & how you intend to use it to get from the previous lick to the next one. Dave's tutorial shows how to connect some triads in a chord progression. My tutorials will how you how the basic I-IV-V progressions are connected across the fretboard.

But most of that is just being familiar with which triad shapes makes which sound. When you first start using them, just play whatever one you can. Once you get familiar with all of them, then you will have the experience of knowing what they sound like & which one you desire the sound of at any given time. But until you start practicing & using them you won't know the sounds. Make sense?

[quote=KillboyPowerhead]

2) The same triad note can be done on high strings or on low strings and i don't know the best practices about how to combine them.

Again that's a matter of personal musical preference that is hard to know until you have a lot of practice & experience using them.

It's kind of like asking which voicing of a chord you should use. It depends on the song, the other instruments, what effect you are going for & what your musical preferences are.

That's why it's important to learn all the notes, then all the possible triads, then learn solos by players you admire to gain experience at how they work.

[quote=KillboyPowerhead]

So i tried without luck to find out here on guitartricks and on the web a sort of "meat and potato" guide that helps you visualize how to combine triads in an easy way when you're improvising, something like the "L shape" bar chords rule if you see what i mean

I have these tutorials on improvisation. But they are aimed more at using a scale to target chord tones.

https://www.guitartricks.com/tutorial.php?input=876

https://www.guitartricks.com/tutorial.php?input=483

https://www.guitartricks.com/tutorial.php?input=491

But, for what it's worth, the L shape works just fine up the fretboard. The only thing is you have to compensate for the G to B string tuning.

For example, in the key of G.

E ||---|---|---|---|---|---|---|-4-|---|-5-|---|---|---|---|[br]B ||---|---|---|---|---|---|---|-1-|---|---|---|---|---|---|[br]G ||---|---|---|---|-4-|---|-5-|---|---|---|---|---|---|---|[br]D ||---|---|---|---|-1-|---|---|---|---|---|---|---|---|---|[br]A ||---|---|-4-|---|-5-|---|---|---|---|---|---|---|---|---|[br]E ||---|---|-1-|---|---|---|---|---|---|---|---|---|---|---|

Or if you start with the root on the A string. For example, in C.

E ||---|---|---|---|---|---|---|-1-|---|---|---|---|---|---|[br]B ||---|---|---|---|---|-4-|---|-5-|---|---|---|---|---|---|[br]G ||---|---|---|---|-1-|---|---|---|---|---|---|---|---|---|[br]D ||---|---|-4-|---|-5-|---|---|---|---|---|---|---|---|---|[br]A ||---|---|-1-|---|---|---|---|---|---|---|---|---|---|---|[br]E ||---|---|---|---|---|---|---|---|---|---|---|---|---|---|

All patterns have to add an extra fret up for the G to B string since they are tuned a third apart (4 frets) instead of a 4th (5 frets) like all the other sets of strings.

That's also an example of how learning all the notes by expanding the octaves works! :)

Hope this helps. If you have other questions please ask! Best of success with triads!