Throwing my hat into the mix, if no one else has suggested it, purchase/download a book that details orchestration techniques and practice. Half of getting orchestral music on a DAW to sound realistic is the knowledge of what an instrument can do, or how instruments are used idiomatically. The best sample libraries, for example, won't tell you when a downstroke will typically be performed in a string section, or how the woodwinds will breathe with a particular phrase, but they WILL supply you with better tools to emulate these techniques and sounds, when you do know. Snappleman is definitely right in the regard that proper use of the samples is key, and learning orchestration technique helps dramatically in that regard. Rimsky-Korsakov's "Principles of Orchestration" is a well known classic, in this regard, if you want a place to start.