Advice How to Ensure Seat Availability on Indian Railways?

I'm planning a trip to India and will be making some train journeys as well. I've been reading on the forum about the challenges in getting an available seat on Indian Railways. How accurate is this information? If it's true, how far in advance should I book my seats for my journeys? Also, what are the best strategies to ensure seat availability for my planned train journeys? Any tips or personal experiences would be greatly appreciated.