I usually practice sitting down, mostly because it's more comfortable, but that's just my prefrence. It's really better to play songs at home the way you will perform them/play them in a group(standing up if you'll be standing up, sitting down if you'll be sitting down). It kind of helps to be more comfortable and able to focus on the music. (or at least, that's what I think
)
Another thing is that while it's good to keep your violin in it's case if you don't have a place for it where it can be out and be safe, if you do, it's good to keep it out, like in a holder or stand. That way if you're walking by and see it there you might get the urge to pick it up and practice. And even if it's just for a few minutes, 15 minutes 4 or 5 times a day adds up to an hour of practice/play! Besides, it can also make it a little more enjoyable, since you don't have make yourself practice. It makes it what it should be;
play time in stead of
chore time.
) I only do the scales if my fingers are just not landing where they should... 
. Length of my "practice" varies based on what else I have to do and how much my back hurts...(playing the fiddle really makes my back ache...I haven't learned how to relax yet with this instrument! 
)
