First, be sure to sign up with Google AdSense, Amazon and/or eBay.
Improve on older hubs, write new ones, pick topics people are interested in (though sometimes topics YOU are passionate about are enough to pull in readers), keyword where you can and promote your hubs online...
You will not make a ton of money, but over time, you will see some profits. I hear there are people around here making a few hundred a month -- though I can't prove it.
I make more through AdSense than anything. It isn't enough to quit my "day job" but the amount is increasing -- I think that is because I actually started writing again! Good luck to you and welcome to HubPages!