String section is the main section in a symphony. It is not just because of it's biggest section in an orchestra, but namely, because of its sound versatility. I would say, strings play similar role in the orchestra like piano in the composer's study room - a must.
It is fairly easy to resound the strings: there are only a few things which, if kept, may let practically anything sound well. Below, please, find some notes and suggestions from my experience:
Violins: while there is no difference between the 1st and 2nd violins sound (except the pan effect), there is no reason to cross the staffs and write 1st violin lower the 2nd and vice versa. Think about the 2nd violins rather as about the lower violins, less expressive in the performance and less technically skilled than the 1st violins.
Violas: thanks to the middle registry tone range, a bit covered sound, less extensive group in the orchestra and usually with worse technical abilities, many composer considered violas as orchestral pads - playing just the harmony. However, if doubled with e.g. french horns, they can play nice expressive melodies, as well.
Cello is probably the most all-round instrument in the orchestra. Its sound can be both soft and sharp, and usable in all registries. Cellos should be considered "the 1st violins" on low registries.
Double bass: there are many jokes about the double bass play technique and sound. Its namely because of they usually produce very muddle sound with heavy-handed technique. If writing for a double bass, think of the sound of subwoofer. To get sharper sound, use it doubled namely with percussion (timpani), low piano (great colour) and/or low brass.
Notation: I would strongly suggest to everybody to spend some time on "debugging" the score and parts in accordance with the "Principles" as well as the general notation rules (see my earlier post, "general conductors comment"). The more time you'll spend on reviewing the parts, the more time you'll earn on rehearsals and/or recording. As far as for the strings notation specifics: please, don't use the 8va--- lines, as most players did always complain of that. The 1st violins are used to read even the highest positions quite comfortable, and for violas, celli and double basses, switch rather for an upper (treble) clef. Although these octave transpositions may - in general - look easier to read, string players rather rate it confusing.
Divisi: in orchestral parts, double stops are usually supposed to be divisi. Therefore, I would suggest to note rather "non divisi" technique instead of "divisi".
Bowings: unless you are an experienced string player, don't spend much time trying to write correct bowings. String players will most probably change it, anyway. Good bowing is a challenge even for string players. Moreover, it is also a bit internal question at every orchestra (have a look into the parts, how many changes were made on bowings over the years in every orchestra....)
Legato, staccato, etc.: it is easier to write general expression notes, than work out every single note in the score (usually, this is the case of computer notation - play loopback). Moreover, it is also much easier to read for both the conductor and players.
Pizzicato: this technique has a few limitations - it can't be too fast, and changes between arco and pizzicato will require a little preparation time (similar to a "breath")
Skips and jumps: most common problem in orchestral scores today. Although on sample libraries, all jums and skips are allowed, in real life, they aren't. Jumps over 1 (1 and 1/2) octave are practically unpossible to play in a section, all together and in tune.
Fast arpeggios: although this technique works well on piano, it is one of the most difficult and totally far-fetched technique for strings. If possible, try to use alternate techniques (e.g. tremollo) instead of this. If you still need to go with arpeggios, try to not exceed, say, one octave (one way) or use the arpeggios continuously, in countermovement (e.g. up and down, up and down etc.).
Sound effects: if you feel there is the need of string effects, think about those with sharper sound, suitable for sectional play. These are e.g. pizzicato, "Bartok" pizzicato, sul ponticello, col legno, etc. Softer effects, like con sordino, sul tasto, harmonics, etc. would sound well rather in solo parts.
Virtuoso techniques: e.g. left hand (Paganini) pizzicatos, fast double/tripple stops passages (non divisi), special bowings, etc. is probably best to omit at all. These efects are mostly unsuitable for an orchestral section: partly because of the orchestral players aren't necesary that soloists, partly, because of these efects sound at best in a solo parts or chamber music. Note, that composing mastery is usualy not in the writting of complicated parts (the less for an orchestra), but on "clever written parts', they will "sound well" already at the first rehearsal.
Glissando: unless it is in a slow tempi or in a contemporary "play-whatever-you-want" composition, I would rather suggest to use notated fast runs. Glissando in a section often sounds rather like low quality orchestra, it can't play in tune and all together. But this, I doubt, could be considered as an "effect"...