Describe an event rather than a feeling
A note that says bad practice gives tomorrow no direction. A note that says I entered the second chorus one beat early identifies a solvable problem. After playing a song with synchronized lyrics and chords, write the section, the event, and the likely cause. Keep observation separate from explanation: losing your place is observable, while blaming concentration is a guess. Include one detail that worked, such as a clean opening or steady final verse. You need a record of repeatable strengths as well as a list of repairs.
Attach one small experiment
For each problem, choose a test that takes only a few minutes. If you rush a chorus entrance, count the last two bars of the verse aloud before playing into it. If a chord feels wrong, compare the recording and two plausible voicings rather than drilling the label unquestioned. If you lose the lyric position, identify a unique phrase before the confusing passage. Write the experiment beside the observation in an ordinary notebook or document. Do not assume the song player includes a journal or a particular annotation feature.
Close the loop at the next rehearsal
Begin the following session with yesterday's experiment before doing a full playthrough. Record whether it helped and what evidence supports that judgment. Three accurate entrances in isolation are encouraging, but also test the transition during a complete verse. Keep the log brief enough that writing does not replace playing. Once a week, scan for recurring patterns across songs: perhaps every error follows a long held chord or a glance at your hands. Choose one shared habit to address. Archive resolved notes rather than carrying them forever. A useful journal makes the next action easier to choose, not the previous session harder to judge.
Keep comparisons within the same musical task. A clean chorus in a familiar key and a hesitant bridge in a new key are different challenges, not evidence that your playing has suddenly deteriorated.