Over the years I realized that sometimes the hardest part of practicing is getting the instrument out. If you play the piano, this won't necessarily be the case, but if you play something smaller like the violin, then you might be shaking your head in agreement right now.
To combat this problem and promote more spontaneous practice, we keep our instruments out and readily accessible.
I know this is not possible for everyone, especially those with babies around, but consider how you might make your instrument more accessible.
My girls know that after breakfast we head upstairs to brush teeth and hair....then we head to the violin room for practice. We have an unspoken rule that whoever gets there first, gets to begin playing.
I also love to hear my girls occasionally pick up their violins and practice without any prompting. If our violins were tucked inside their cases, I'm sure this would not happen.