You've perfected and polished every last word of that presentation, elevator pitch, or sales spiel. It's so ingrained in your memory, you're certain that your delivery and your body language are absolutely spot-on.

That's not what your audience or conversational partner sees, though. Instead, they're looking at someone who appears nervous and self-conscious.

The quality of your content is good. But your constantly shifting eye contact and endless shuffling is distracting from your core message.

No matter how refined our words, our nonverbal cues often speak much louder. Here are six body language mistakes that are undermining your confidence, so you can stop making them immediately:

1. Avoiding Eye Contact

Failing to make solid eye contact--whether it's with just one conversational partner or select people in a larger audience--is a surefire way to appear nervous and unconfident.

Instead, focus on holding someone's gaze when speaking. It not only makes you appear more self-assured, it also makes your words that much more engaging.

2. Making Gestures Toward Your Body

You know that standing there like a rigid robot wouldn't do you any favors. But making hand gestures is only half the battle--you need to be sure you're making the right kind of motions.

When we're nervous, many of us have the tendency to make small, minor gestures inward toward our bodies. Resist that inclination, and instead commit to your movement--making bigger motions toward the person you're speaking to. It'll instantly up your confidence level.

3. Slouching

Your posture is a key indicator of how you're feeling. When we slouch, we're attempting to make ourselves smaller and draw less attention.

Obviously, that's not the goal when you're speaking. So pull your shoulders back, pick your chin up, and deliver your words with a stance that exudes confidence and professionalism.

4. Shifting Your Feet

Similarly to your posture, your feet also say a lot about your level of confidence. If you're constantly rocking on your heels or shifting your standing position, you only look fidgety and apprehensive.

So plant your feet shoulder width apart (as long as it feels comfortable!) and focus on staying there. Yes, some speeches or presentations lend themselves to some movement across the stage. But if you're feeling particularly jittery (or nervous about tripping), you're better off staying put.

5. Neglecting Facial Expressions

Yes, there's a lot to think about when it comes to oozing confidence. But you can't become so focused on the rest of your body that you forget about the one thing everyone is actually looking at--your face.

We've all seen those speakers with totally deadpan expressions, and you don't want to be one of them. Practice reflecting your message on your face, and--when it's warranted--smile. It's the best way to instantly appear more confident.

6. Overthinking Your Handshake

A limp handshake is the worst--you've heard it time and time again. Unfortunately, many people take that advice to the extreme, causing their handshakes to reach a nearly bone-crushing level.

Taking your handshake too far in either direction is going to undermine your level of confidence. So don't overthink things. A natural, politely firm handshake is your best route.

Whether it's a big presentation or an important networking event, you want to do your best to radiate confidence. But that can be easier said than done--especially when you add nerves into the mix.

Stay far away from these six common body language mistakes, and you're sure to send a self-assured and poised message.