It's absolutely critical that you practice at least something every day! What you practice is also critical. Just playing a few tunes, or jamming with friends is only one part of daily practice (the fun part!).
Divide your practice time into three "parts" of equal length. That means, if you practice 30 minutes a day, each parts will be 10 minutes. It's scalable (pun intended), so if you practice an hour, each part is 20 minutes and so on.
First Part: A Daily Scale "Set"
each day play a different scale set from the circle of fifths (if you're practicing bluegrass music), otherwise a different tonic set using the 7 church modes
practice 2 octaves, use 4th fingers always
remember where to shift when playing in 3rd and 4th positions
fiddlers: practice the 4 bowing patterns with each scale
mandolinists: practice the 5 picking patterns with each scale
circle of fifths: practice the major AND the relative minor with each set
modes: practice all 7 modes
practice the arpeggios for each scale (1,3,5,8)
Second Part: New Material
Sight read assigned new material
Practice first measure, slowly, without ornamentation or bowing until you have the notes down, then go on to 2nd, 3rd, 4th measures
After you have the measures well established, add any ornamentation and bowings as indicated in the sheet music or by your instructor
Don't try to learn the whole piece in one "chunk". It's better to master one 4 bar phrase than to play the whole piece poorly
Third Part: Review & Sight Reading
Jam with friends/family
Review old material, work on the hard parts
Sight Read out of the Fiddler's Fakebook or any other book as assigned by your instructor