Keep high-value tiles and flexible middle numbers that can join several runs or sets, since you need melds totalling at least 101 to open.

Higher numbers contribute more points toward the opening threshold, so they are valuable to hold early. Tiles that connect in multiple directions, and the okey joker, give you the most options. Be cautious about discarding pieces that could complete a big meld. Balancing point value against how quickly you can actually form groups is the core skill of building a strong 101 hand.