Playing in Time - Your Foot
Once you can tap your foot in time while playing (this takes practice in your formative years), it can be the best indicator of when your rhythm gets off. If your foot stutters or stalls, this indicates a part of the song you don't own the rhythm of yet. Practice this part of the song in isolation until you can comfortably play the passage without your foot hesitating.
P.S., it doesn't matter whether you tap the front of your foot (ball), back (heel), alternate between the two or tap both feet alternately... as long as something is tapping consistently.
Have a great weekend everyone!