Knowing which articulations to use starts with a knowledge of what the various instruments are capable of playing, and the names given to those articulations. Of course you could learn them by ear, but knowing what they're called, as well as familiarizing yourself with what real players play, in all manner of styles and tempi, is really important.
For example, let's take string four articulation names:
marcato
detache
spiccato
staccato
All of these are considered short bow strokes. However, in some libraries, "marcato" sounds sustain but their attack characteristic is marcato. You'll find the same situation with samples called "detache"; in some libraries the length of detache samples can vary greatly. These kinds of variations exist because there is no singular way for a player to perform them, and the length of any particular short bow stroke is going to change with the tempo, which brings me to spiccato and staccato...
At a fast tempo, a spiccato sample is likely going to sound better, less sluggish, than a staccato sample even though an orchestrator would write the part as staccato. At a slower tempo, staccato notes might be best played with detache or marcato samples (provided they don't sustain too long).
So one of the best things I can suggest is that you get a book or two on orchestration and learn the names of the different articulations. Samuel Adler's "The Study of Orchestration" is great as is the Blatter book on orchestration.