I learned this years and years upon years ago. I shared it elsewhere, figured I would share it here as well.
Bottle too small to give it a proper cleaning? No worries, rice and vinegar to the rescue!
Pour rice into bottle, jar or vase, about a third of the way up. Cover rice with vinegar. Top, or cover with a lid of some sort, and shake vigorously until it feels like your arm will fall off.
Viola! Sparkly clean glass.
Make sure to rinse very well before using.