G.I. Joe always told me 'knowledge is half the battle'. So for the newbies in the hiz-ouse - If you're still shopping for a microphone to suit your DSLR audio needs, you'll probably already find that the Rode VideoMic is a very popular one. I've run my own tests and found that it does perform much better than some microphones going for twice it's price. But before you start throwing down a solid buck, you can read up some other interesting suggestions through the B&H Insights blog that might help you get a bit more 'knowledge' - Go Joe!.
B&H Photo Video Insights Blog for DSLR Microphone Options
So a microphone will help you focus in on a little better sound than just the onboard microphone, but for the best sound processing, you'll want to shop for a portable audio recorder. The in camera audio of the DSLR's are just not up to par for the true audiophile. The link below jumps you to another B&H Insights article about different Portable Audio recorder solutions.
B&H Photo Video Insights Blog for DSLR Portable Audio Recorders
example of Redhead Windscreen on Zoom H4n
The Zoom H1 has become my favorite go to audio recorder for a quick take. I can get this setup on just about anything fairly quickly. I shot a demo about LCW's BigEye viewfinder found here: http://cheesycam.com/quick-review-lcw-bigeye-profinder-dslr-view-finder/ using only the on board microphones and the X/Y stereo configuration sounded sweet. Of course I was in a controlled studio and just like any microphone, it's completely vulnerable to small breezes. The sad fact is the basic Zoom H1 package does not come with any type of windscreen.
If you're wondering about a DIY, I actually had a go and failed pretty miserably. Sure, whatever fuzzy little monstrosity I created made a slight difference, but nothing like a Redhead Windscreen. There's actually different types of fur, thickness of fur, length of fur, acoustically transparent backing, and a bunch of other things to consider for best performance. By the time I got the materials, tested a few, and had wifey sew everything up, I put in more than enough funds where I should have just purchased one. In fact, I did purchase one and wifey to this day gives me dirty looks about wasting her time whenever I strap on the purchased Windscreen. Well you don't start appreciating good gear until go through some of the pains I guess.
So i've been waiting on everyone's favorite brand Redhead Windscreens to finally release a Zoom H1 version. Redhead Windscreen is owned by active Vimeo Member and Audiophile iamkalaniprince. Just a few days ago the Zoom H1 version was announced, and i'm excited to get a hold of a couple since I have multiple H1's. The above video is an example shot with a Redhead Windscreen on a Zoom H4n, but there's a long list of Audio recorders that are supported. You can find more information about RedHead Windscreens at http://www.redheadwindscreens.com/.
Below: Current list of RedHead Windscreens supported Portable Audio Recorders