props to Rosco for their great answer. Some juice will improve over time. Various companies are famous for their steeping time. Backwoods Brew is a great vendor and their liquid usually takes about two weeks minimum to steep. I've found that extracted tobacco liquids need to steep unless the vendor has steeped them for awhile. Most liquids that are simply flavorings squirted into pg/vg are good to go from the beginning. I've got a bottle of Malty Toffee from Backwoods Brew. It's great now and in a week it will be fantastic. One of my favorite vendors is Kick Bass Vapor. Very few of their juice needs to steep. It's good to go when it arrives in the mail. Want2Vape extracts their own tobaccos (and is fantastic!) and they really don't need to steep because they're already pre-steeped.
To describe the best way to steep, just keep it in a dark place away from sunlight and temperature controlled. Some people leave the cap off for 24 hours initially, others don't. Some liquids need a week, others may need months. It's going to be your own adventure and preference. Dark, temperature controlled, and patience are the key to steeping.