Hello there.
When it comes about render speed it's a good idea to keep the objects geometry and textures as low as possible -- well known. Still, it's of humongous use to know this a little in detail. It can considerably boost FPS's to follow simple rules like: which of the following matter most, which less and which are irrelevant?

1. vertices number
2. polygons number
3. objects number
4. texture size

The whole idea behind this is to have a balance between them so to get zero bottleneck.

You're probably asking what does texture size have to do with vertices? Well, I could split a polygon of an object in more several polygons, by extra verts, and use a smaller texture that otherwise would need to be larger to hold the initial single polygon.

I know some of you will say it depends on each particular project but still, there are general rules to start from and then one would bend them as seen fit for a case.

What does your experience or theory say about it?