Quien mucho abarca poco aprieta

[ROBINDESBOIS]

It means that it´s better to concentrate on one thing in particular than doing lots of things at the same time. ENGLISH?

[Perikles]

Don't try to take on too much.

[Rusty]

Look here (http://www.tomisimo.org/idioms/es/el-que-mucho-abarca-poco-aprieta-1228.html).

[poli]

also: Don't spread yourself too thin.