Your Mexican beach vacation was great, but, man, those margaritas sure can put on the pounds. It’s been two months, and you’re still carrying around an extra tenner — despite a new running routine and a lot of #&*&@$ kale. So why isn’t your weight dropping?

It’s like that with energy bills, too. Eighty-nine percent of us believe we’re doing the right things to lower energy costs, and almost half of us think our homes already are energy efficient. Yet, 59% of us say our bills are going up, not down, despite our efforts to economize.

Suzanne Shelton, CEO of the Shelton Group, a marketing agency that specializes in energy efficiency and that did this research, says we’re rationalizing: “I bought these [LEDs] so now I can leave the lights on and not pay more. I ate the salad, so I can have the chocolate cake.” Denial much?

Her research also shows consumers, on average, made fewer than three energy-efficient improvements in 2012 compared with almost five in 2010. It looks like we’re giving in to higher utility bills. But it doesn’t have to be that way.

You just need to know what improvements really will make the biggest difference to lower your bills. There are five, and the good news is that they’re really (seriously) cheap. You can go straight to them here, but there’s also another thing you can do that doesn’t cost a dime — and will drop your costs:

Be Mindful About Your Relationship With Energy

Think about it. Energy is the only product we buy on a daily basis without knowing how much it costs until a month later, says Cliff Majersik, executive director of the Institute for Market Transformation, a research and policy-making nonprofit focused on improving buildings’ energy efficiency.

With other services you get a choice of whether to buy based on price. With energy you don’t get that choice — unless you intentionally decide not to buy. You can take control by making yourself aware that you’re spending money on something you don’t need each time you leave home with the AC on high, lights and ceiling fans on, and your computer wide awake.

Related: Did You Know You Should Never Leave a Ceiling Fan on When You Leave a Room?

That mindfulness is important because your relationship with energy is getting more intense. You (and practically every other person on the planet) are plugging in more and more. Used to be that heating and cooling were the biggest energy hogs, but now appliances, electronics, water heating, and lighting together have that dubious honor, according to Lawrence Berkeley National Labs, based on data from U.S. Energy Information Administration (EIA), the research arm of the Department of Energy (DOE).

Energy is the only product we buy on a daily basis without knowing how much it costs until a month later. — Cliff Majersik, executive director of the Institute for Market Transformation

Being mindful means it’s also time to banish four assumptions that are sabotaging your energy-efficiency efforts:

1. Newer homes (less than 30 years old) are already energy efficient because they were built to code. Don’t bank on it. Building codes change pretty regularly, so even newer homes benefit from improvements, says Lee Ann Head, vice president of research and insights with the Shelton Group.

2. Utilities are out to get us: They’ll jack up prices no matter what we do. It might feel cathartic to blame them (Shelton’s research shows consumers blame utilities above oil companies and the government), but to get any rate changes, utilities must make a formal case to public utility commissions.

3. Energy improvements should pay for themselves. Nice wish, but it doesn’t work that way. When the Shelton Group asked consumers what they would expect to recoup if they invested $4,000 in energy-efficient home improvements, they said about 75% to 80%.

Unless you invest in some kind of renewable energy source like geothermal and solar, you won’t see that kind of savings. (Sorry.) Even if you do all the right things, the most you should expect is a 20% to 30% reduction annually, says Head, which is still significant over the long term.

What does 30% translate into? $618 in savings per year or $52 per month, based on the average household energy spend of $2,060 per year, according to Lawrence Berkeley and EIA.

4. Expensive improvements will have the biggest impact. That’s why homeowners often choose pricey projects like replacing windows, which should probably be fifth or sixth on the list of energy-efficient improvements, Shelton says.

There’s nothing wrong with investing in new windows. They feel sturdier; look pretty; can increase the value of your home; feel safer than old, crooked windows; and, yes, offer energy savings you can feel (no more draft).

But new windows are the wrong choice if your only reason for the project was reducing energy costs. You could replace double-pane windows with new efficient ones for about $9,000 to $12,000 and save $27 to $111 a year on your energy bill, according to EnergyStar. (The savings are higher if you replace single-pane windows.) Or you could spend around $1,000 for new insulation, caulking, and sealing, and save 11% on your energy bill, or $227.

The 5 Things That Really Work to Cut Energy Costs

1. Caulk and seal air leaks. Buy a few cans of Great Stuff and knock yourself out over a weekend to seal around:

Plumbing lines

Electric wires

Recessed lighting

Windows

Crawlspaces

Attics

Savings: Up to $227 a year -- even more if you add or upgrade your insulation.

Related: Lots of Homes Also Have This HUGE Air Leak

2. Hire a pro to seal ductwork and give your HVAC a tune-up. Leaky ducts are a common energy-waster.

Savings: Up to $412 a year.

3. Program your thermostat. Shelton says 40% of consumers in her survey admit they don’t program their thermostat for energy savings. She thinks it’s even higher.

Savings: Up to $180 a year.

4. Replace all your light bulbs with LEDs. They’re coming down in price, making them even more cost effective.

Savings: $75 a year or more by replacing your five most frequently used bulbs with Energy Star-rated models.

Related: LED Bulbs Are Confusing, But Here’s a Guide to Help

5. Reduce the temperature on your water heater. Set your tank heater to 120 degrees — not the 140 degrees most are set to out of the box. Also wrap an older water heater and the hot water pipes in insulating material to save on heat loss.

Savings: $12 to $30 a year for each 10-degree reduction in temp.

NOTE: Resist the urge to total these five numbers for annual savings. The estimated savings for each product or activity can’t be summed because of “interactive effects,” says DOE. If you first replace your central AC with a more efficient one, saving, say, 15% on energy consumption, and then seal ducts, you wouldn’t save as much total energy on duct sealing as you would have if you had first sealed them. There’s just less energy to save at that point.

Bonus Tip for More Savings

Your utility may have funds available to help pay for energy improvement. Contact them directly, or visit DSIRE, a database of federal, state, local, and utility rebates searchable by state. Energy Star has a discount and rebate finder, too.

Related: Fun DIY Projects to Cut Energy Use