Be confident - You will be able to better project your voice if you are confident. If you lack confidence, try recording your voice and listen to how you sound. Then try recording your voice and speak with confidence, then compare the recordings and decide which voice you desire.
Talk slower - It will help project your voice from your chest
Vocal Exercises - Do some vocal exercises, humming, etc. You can find vocal exercises with a simple google search
Keep your head up when you speak - If you do the exercise mentioned on this page, you'll notice why keeping your head up when you speak helps alot in projecting a deeper voice.
Practice - It doesn't just come out of nowhere. You need to spend time alone and play around with your voice, and see what you can do with it. You can also take this alone time to do vocal exercises.
Talk from the back of your throat - Talk from the back of your throat and focus on your R's.