What would you like to know about slurs and bow directions? As a cellist, I don't always perform the markings on the page, but bow markings and slurs can inform how I shape a phrase or build the atmosphere of a piece. So when you write articulation, first worry about phrasing--then, you can worry about the practicality of each marking. While there is no single correct way to articulate music for bowed instruments, some things are simply more convenient. For example, if you want a crescendo over the course of many notes, slur those notes and make it an up bow. Conversely, if you want a diminuendo, make it a down bow. If you want rapid staccato notes, you can write up-bow staccato (write a slur over a series of staccato notes and make it an up bow) or simply write separate notes.
I think the last thing to keep in mind is this: the bow is to a string player as breath is to a singer. If you are wondering how many notes to put on one bow, try to sing it! If you find yourself out of breath, you may want to switch directions with the bow. But skilled players can express phrasing effectively even while having to change bows--Brahms certainly takes advantage of this when writing his string parts. In the attached picture, notice that the upbeats (normally played with up-bows in other pieces) are played with down-bows in this excerpt to accommodate the crescendo starting in the next measure.
To truly learn about writing for bowed string instruments, you have to be able to think like a string player. Listen to recordings while following along scores and string parts, and you should be good to go!