Medicare is a fantastic resource for retirees, offering healthcare coverage that would be prohibitively expensive if purchased through a regular health insurance policy. However, Medicare isn't actually free... and it may not even be cheap if you pick the wrong plan. If you select your Medicare plans using the following criteria, you'll be able to minimize your monthly premiums -- and can end up saving significant moola as a result.

1. Choose Medicare Advantage over Medigap
Medigap plans are a sort of aftermarket add-on for original Medicare. They pay for many of the original Medicare deductibles (the amount you're required to pay out-of-pocket before your insurance kicks in), and also provide coverage for services that aren't included in Medicare Part A or Part B. Medicare Advantage plans, on the other hand, work more like the health insurance policy you likely had before you retired. These plans replace original Medicare as well as providing additional coverage, and they typically feature both deductibles and co-pays (the portion of a medical expense you're required to cover yourself, even after you've met your deductible for the year).

Medicare Advantage plans tend to have significantly lower premiums than comparable Medigap plans, in part because the Advantage plans typically require you to shell out more for deductibles and co-pays. Thus, choosing Medicare Advantage over Medigap should reduce your Medicare premiums. However, it's important to look at all your cost factors when making this decision -- if you expect to have a lot of medical expenses in the near future, a Medigap plan may work out to be the cheaper option overall because the lower deductibles mean the plan will pay more of your expenses than a Medicare Advantage plan would.