The hardware includes a texture cache. As with all caches, the secret to getting the best performance is to try to operate with cached data as much as possible. Consequently, your first order of business when working with textures is pick appropriate texturesand textures of appropriate sizesto ensure you don't end up running out of cache. One 128x64 texture fits fine in the cache.
Another trick that helps is to sort your render commands first by texture object and then by state vector. Grouping render commands by texture object helps keep relevant textures in the cache for as long as possible during the rendering process.
While on the topic of textures, it's a good idea to use an appropriate filtering mode for your textures. Linear filtering is fine as long as the texture's cached, but if your texture doesn't fit in cache or for large textures, you're better off with nearest filtering, because the cost of linear filtering can be as much as 15 percent.
A final trick that falls into the category of textures is to simulate lighting with textures. While the OpenGL ES interface has support for lighting, complex lighting can cause enormous slowdowns (up to forty percent in some cases). If you can get away with pre-computing lighting into the texture bitmaps and rendering your models with the appropriately-lit textures, you're better off.
It's Still in Your Hands
While OpenGL ES promises 3D portability to gaming and graphics developers, it's not a panacea. As the developer, you're still responsible for determining how your application performs. Making an effort to tune your implementation will pay off, not just on Brew, but as you port your application to different platforms as well.