An excellent habit to form on your turn of play is to PICK a tile from the wall, RACK the tile IN your rack, and DISCARD ANOTHER tile from your rack.
Do not discard the tile you just picked. This method will give you some time to consider the newest tile in your rack. We have all inadvertently discarded a tile we should have saved, even for its use in a back up hand. We may have had a much less useful tile we should have discarded. Getting into the practice of discarding a tile other than your most recent pick may allow you to keep more options open. Continue to discard a different tile than picked until you can no longer do so. When you are almost ready to Maj, you will only have one tile left in play to discard from your rack. And, of course, when you have NO tile to discard, you should verify your tiles and CALL for Mah Jongg!!!