Don't use WD40! It removes the grime but won't lubricate long term. I suggest instead to use a ceramic or teflon chain lube (for bicycling) as it will stay longer.
I use this:
Finish Line DRY Teflon Bicycle Chain Lube, 4-Ounce Drip Squeeze Bottle https://a.co/d/2uzpJzI
