Optimizing Mesh

I had the same problem, here are some reasons.
Mesh is not managed(video, system memory)
Optimize is done wong.
Too slow rendering call.(hirachy is too long)(too much matrix mults)
Much redundant renderstate changes.
To much drawindexprimitive calls.
No texture compression.
Vertex Data is too big.(on slow cpu,with slow ram,2 level cache slow,software vertex processing)
Overdraw is too much.
Try optimise for 1 strip.(is a little slower on hardware,but much faster on software)

Another possible reason:

The mesh is already near-optimal.

Thanks.
what do u mean by texture compression ? do u mean using texture with smaller size ?
what is overdraw ?
how to optimize for one strip ?
thanks