Medicare's annual open enrollment period began on Oct. 15. And between now and Dec. 7, you have an opportunity to make changes to your existing coverage. That includes getting a new Part D drug plan.

But whether it's your first time navigating open enrollment or your 17th, the reality is that choosing the right Part D plan can be tricky. Here are three tips to help you along.

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1. Make a list of your current prescriptions

Before you can begin to explore options for Medicare Part D coverage, you'll need a comprehensive list of your current medications. Round up those pill bottles and take note of not just your medications themselves, but the quantities you tend to get them in.

If you notice that you're taking a lot of name-brand medications, you may want to talk to your doctor about switching to generics before exploring your plan choices. If you learn that that's an option, it could significantly impact the amount of money you spend for drug coverage.

2. See what different plan formularies look like

In the course of looking for a new Part D plan, you may be inclined to compare your choices by premium cost. But focusing on premiums only could end up being a costly mistake. It's just as important to look at what your specific medications will cost under different plans.

Medicare Part D plans use formularies to group medications into different tiers. And the higher the tier, the more expensive a given drug can cost.

In the course of reviewing your plan choices, it's really important to see which tiers your specific medications are grouped into. That's what will determine the amount you pay.

3. Use Medicare's plan finder to compare your choices

The idea of finding a new Part D drug plan might seem daunting. The good news, though, is that Medicare makes it pretty easy if you use its plan finder.

Medicare's tool lets you input the specific medications you take, along with your geographic location, to get a list of plan choices. From there, you can study each one and do some comparisons.

In the course of doing so, make sure to pay attention to plan ratings, as those are indicative of how happy existing Medicare enrollees are with their coverage. The ratings system couldn't be simpler. It works on a scale of one to five, with one being the lowest score and five being the highest.

It's important to choose the right plan

Some seniors are forced to go to the extreme of cutting back on the medication they need due to issues with affordability. And that's the last thing you want.

Identifying and signing up for the right Part D drug plan could spell the difference between being able to pay for your medications in full versus having to skimp. So take the time during open enrollment to review your choices, and aim to start sooner rather than later so you aren't forced to rush your way through the process.