Start at the pit with a notepad and the pump's install year, taken from its plate or your paper. That year is a planning input. Nothing in this walk-through says the pump will fail.
Your first entry is run frequency. During a wet spell, watch how often the pump starts over a fixed stretch of time, such as an evening. Write the count. On your next visit, count the same way and compare. A change in starts is worth a line in the log, even when the pump still clears the pit.
Next, listen. Note whether the motor start sounds the same, whether there is a longer hum before the pump engages, and whether the float or the discharge pipe rattles during a run. Describe each sound in plain words, such as rattle near the discharge or longer hum before start. Plain words are easier to compare later.
Check the float. It should move freely on its arm or rod and rest without catching on the pit wall, the discharge pipe, or the cord. Write down any catch you see and where it happens.
Check the discharge. Once the pump runs, go outside and look where the water exits. Note the strength of the flow and whether it drains away from the foundation. A flow that seems weaker than in your earlier notes goes in the log.
Watch the return. After a run, see whether water drains back into the pit quickly. A quick return is a line to write down, along with roughly how long it took.
Clean the pit screen and remove loose debris before the next wet period. Before you reach into the pit, turn the pump off at its breaker and make sure the water is still. Do not work near a live pump.
Keep the notes in one place with the install year. If the same change keeps showing up across visits, a qualified service person can use your log to begin their own check. The log is not a diagnosis and not a repair plan. It is a record that shows the next person what changed and when you first saw it.