The concept of intonation goes way beyond playing a note of the correct pitch. It encompasses other aspects that can greatly affect it. Intonation consists of 3 equal parts: Tune, Tone and Time. These three parts must all be present and balanced for true intonation to occur. If the note is out of tune, not fully sounded or not played in correct time, it will not sound "right".
So you may ask, “How do I work on this?”
The first thing to do is work on each part separately and then combine them.
Tune: You fretted players can still benefit from this as it is a great ear training exercise. Play arpeggios, pentatonics, scales, etc. against a drone of the tonic key (many websites exist that can furnish this). Play them all over the board. Be VERY critical. Only PERFECT notes are acceptable. You are training yourself to play perfectly against the key of the song or chord you are supporting. You can add a metronome for added challenge..but play it SLOWLY!!!! You are trying to achieve accuracy!!!
Tone: Make sure you’re playing posture is correct and that every note is full and round and clear whether fretted, fretless or upright. ..arco or pizzicato. If you use vibrato, make sure it is clear, thick, round and relaxed. Tone is not just amp settings, string gauge, etc. It is proper execution and posture…I work on this EVERY day!!!
Time: Practice EVERYTHING you do with a metronome....see my mini lesson on time. If what you play is rushed or drags or feels unsettled, it is not intoned. Play slowly and accurately..it is VERY important to not only be in time, but to KNOW time!!!
Lastly, play something you know keeping the “Triumverate” in mind. Record yourself and listen to your improvement over time. I did this for years and it was very humbling and rewarding at the same time. Keep in mind true intonation is a skill that needs to be maintained and honed throughout your playing career and you progress will depend on how diligently you adhere to the concept of the Triumvirate.
Lots of Luck!!!
Feel Free to ask Questions.