Keep the brightest pieces for offense. Use them when they can affect the largest number of your opponent's pieces. Try for the largest differences, such as red on yellow; or bright blue on green. Placing a very bright color on a tile that affects no other tile is wasteful. Instead, use tiles in areas that will always have an effect on your opponent's pieces. The player who places the tile receives the advantage of it affecting the surrounding ones. This will change the colors of your opponent's pieces and thus lower their score.