There are so many different elements to a more polished vocal image. But the one element that helps to instantly improve your personal presentation is  Enunciation. Oh I know we take it for granted, we all assume that people understand us, but sloppy enunciation is actually considered to be one of the most irritating of all bad speech habits.  

Failing to enunciate each syllable in each word and actually pronouncing the endings may make it difficult for listeners to understand us. The few seconds it takes to decipher what we are saying may cause them to miss a part of our message. Cutting off the endings of words and eliminating consonants may subconsciously give the impression that we are sloppy or even uneducated. Crisp, clean speech is a joy to listen to and in a world filled with sloppy speech, may subtly convey that you are thorough and sharp.  

The most common habits are dropping the 'g' in words ending in 'ing' like thinkin' versus 'thinking'. 'Er' often morphs into 'a' like leatha' instead of leather. It's easy to say these words correctly in isolation, but it's when they are placed in the middle of a sentence that we have to be more cognizant.  

Here's a tongue twister for you to practice in the mirror 15 minutes a day to help train your mouth and mind.   

He's buying & selling a yellow feather but she's thinking red leather is better.  

When practiced with perfect enunciation this is a tough one, especially as you speed it up. The goal is to get your mouth moving, notice how you have to use your facial muscles to say it correctly. This helps to create muscle memory that can eventually improve your everyday speech.