Try to retain a few red tiles on the level. If you consume too many of them, even higher numbers will begin appearing and force the pace to increase and crowd you in. Leave just enough red tiles on the level to maintain proper speed. Target low value green tiles. Keep as few small number tiles on the level as possible in order to have new tiles have larger value. Each tile is worth 1 point, and although they will lengthen your snake at times, they can also cause chain reactions that can shorten it and save you.