Certified GKH Gardening Expert
Place your potted Lavender in good location. This means as much sunlight as possible with good air circulation. A sunroom is great for this although you could rig some broad spectrum or fluorescent lights up in a basement if you cannot find a sunny spot. Houses in winter tend to be drier due to heating so humidity usually is not a problem.
Make sure to check on your Lavender plant periodically and as for watering try to be lax about it erring on less and not more. Allow the top inch or so of soil to get bone dry. Rotate the pot every week so it receives uniform light and air.
Over watering potted Lavender grown inside is the main reason for plant fatality. Your plant will not need as much water and definitely not any fertilizer until warm spring weather returns. Be sure to wait until the last spring frost date for your area or you overwintered your potted Lavender for nothing!