Cut your draw calls by combining sprite sheets.
From Tomáš Rychnovský: "Everybody with at least short experience in game development came across sprite atlases. Its benefits are in merging multiple sprites into one large bitmap and so decreasing draw calls. We can simplify draw call as request to GPU to draw something with some set of parameters. One of these parameters is also texture. Changing any of parameters results into quite expensive setup on GPU side (flushing current work and doing setup for different set of parameters) - this is reason why to build larger textures made from individual sprites.
Currently there is lot of tools, that help you with creating sprite atlas from individual sprites. But, when it comes to fonts, the situation starts to get complicated.
For creating fonts I am using on-line tool Littera. This tool is great, but when you are exporting your font, you already get some atlas that contains your font characters. Alongside, you get file with characters metadata saying where in atlas is character positioned, how big it is ..."