First, planting. You need to chose your mix. I personally just use a mix of Miracle Grow and perlite in a 1:1 ratio. It doesn't drain as well as the gritty mix or 5-1-1 mix. You can find more info about those if you search "gritty mix" or "5-1-1 mix." A lot of people here use those, but you have to get a lot of ingredients for it. Also, don't plant it until four weeks after you get it. If you do the Meyer may lose leaves.

sun: Meyers need a lot of sun. Try to let it get at least 6 hours of sun a day. Rotate it once or twice a week so it gets lots of sun all around. You can slowly transfer it outside when in gets warm, but Meyers are extremely sensitive to light changes.

Spider mites: you can control these pests with neem oil. Spray the leaves, preferably outside, and they should be gone after a few treatments.

watering: water indoor potted trees when they are still slightly moist. I water mine every 1-1/2 weeks.

dropping leaves because sun change: there is nothing you can do to help the leaf drop. When Meyer lemons are introduced to drastic light changes, they will lose almost all of there leaves. They will grow back.