One of the most important concepts in R is vectorization. This is so different from what one does naturally in languages such as C, Fortran, Pascal or even some other scripting languages such as Maple. For good R usage, think vectors. In this respect R is similar to APL and Mathematica.
By think vectors we mean you should try to avoid doing working with the elements of a vector, matrix or array and instead try to work with the whole thing. And you should try to structure your computations in terms of vector, matrix or array operations.