What I do is put some of the 'dirty' media from an established filter into the new filter, including some poly fiber, which I use in all my filters for water 'polishing'. Then I stock and feed the new tank lightly at first. Theoretically, the beneficial bacteria in you filter can multiply every 24 hours or so, I like to give it a few days to a week before adding more fish or feeding more. Testing ammonia/nitrite will let you know without guessing-- alternately I've used Seachem's Ammonia Alert cards in new tanks, I've double checked them with an ammonia test and they do work ime. The ammonia card has an advantage in only reacting to ammonia in its toxic form while most liquid tests react to total ammonia. While I look for zero ammonia anyway, technically, with a standard test you need a pH conversion chart to ascertain the actual percentage of ammonia (toxic) vs ammonium (not toxic). Neutral or lower pH skews more toward the non-toxic form, higher pH skews more to toxic.
That's the beauty of the ammonia card, it reacts only to toxic ammonia, doesn't tell you nitrite, though.
If your old tank has gravel you can also transfer some of the gravel, since that also harbors part of your bacteria colony in a tank. I've also put a bag of gravel from an established tank into a new filter to seed it.