Just play loud for a couple of hours - preferably big, crunchy, chunky chords.

If you're in a hurry you can also put any kind of noice or hum through it - for example, the loud buzz you get when you touch the tip of your guitar cable. This is best done by cranking the amp then sticking it face down in a wardrobe or something, muffled with pillows, towels etc.
Nope that's about right. For the first hour or two of playing it'll sound like a cheapo cardboard speaker, but once you've gt past that it'll be a slower, less pronounced improvement, a little like the way a new acoustic improves over time.

The higher the volume, the quicker it'll improve. After two or three hours of high-volume use it'll sound fine with a band, andby the time you've covered a few gigs or practices it'll sound pretty damn good.
So your current speaker which should sound like cardboard in comparison sounds as good as your old Jensen-speaker. Things are looking great for you.
If you really want to break it in quickly there's a method which involves a Variac and no playing and takes under a day...
The Laney Thread are big and clever. No exceptions.
You find the max power handling of the speaker, divide by 3, and apply an AC source of that many watts, considering the ohmage - I assume yours is 8ohm - and the handling being 75w, you'd apply 25w of power. At 8ohm that's 14v.

Not sure exactly how long you do it for, but it is meant to break it in very quickly.
The Laney Thread are big and clever. No exceptions.