When you sign up for Trim, they immediately begin analyzing your spending and look for ways to reduce it. They’ll call your internet service provider and negotiate you a better deal on the same service. Same for your cable package (or any other recurring service you have). They’ll also look for hidden or otherwise forgotten about subscriptions and cancel those if needed. Think of them as your bill guard dog. No one gets by without their permission.
Online website review companies like UserTesting allow you to review and test professional web sites from the comfort of your own home. You don't need any professional certification to do so - just be computer efficient, be diligent, take instructions well, and be good at writing up your thoughts on a given web site. Plenty of Fortune 500 companies partner with UserTesting, and regular web site reviewers can make up to $30 per hour.
Try night filling for supermarkets/large stores, supermarket/retail cashiers, vacation seasonal factory work/seasonal fruit picking, night reception in a small hotel, cleaning, gas station attendant, making crafts or artwork and selling online, YouTube video making (but it needs to be popular), dog walking, babysitting, tutoring, housesitting, etc. There are many part-time options where college students are favored because people get to pay you less than a service provider but get to know you better, so it's a friendlier arrangement.
If you have to pay it now, you have to take out a loan, ask for an advance on your salary or borrow money from friends or family. If it can wait, the amount will accumulate interest until you pay it back. If it's just one month out of twelve, and the other eleven you always have money left over, there's not really anything to worry about. Put the left over money aside to pay this month's expenses. Other than that, there are only two things you can do: spend less, or earn more. Sell your car, move to a smaller place, get a roommate. Cut whatever expenses you need to break even. Try for a second job, a raise, or sell something you make.
Regardless if you need to earn some fast cash or we're just talking about making money in the grand scheme of things, there's an important psychology that needs to be mentioned before getting into the strategies. If you study Freud's model of the mind, you'll discover the Psychic Apparatus. It's the three-part construct in your mind that controls all of your behavior.