You're making good progress but there are a few pixel-sins being commited.
You may not even know it, but what you've done with the outlines on the pants is called "sel-out" (selective outlining), it can work in controlled environments where the sprite will always be up against a specific coloured background but ideally you want your sprite to be as versatile and efficient as possible, which means a more consistent outline is the way to go.
Here you can see the effect when put up against different colours, in some cases the edges are smooth, but in most they are made rougher. The same issue persists with his right shoulder and to a slightly lesser extent- his hair. There are a few spots on his arms where you've broken the outlines with selout but for the most part you've done them well.
I can see you don't quite understand how or why anti aliasing works in pixelart, this should help a little:
Anti aliasing:
Step 1:
Here is a selection from your line art, you need to think about the information that these pixels represent.
Step 2:
Here is roughly the information the above pixels should be trying to convey.
You'll notice that even though the image is still broken into "pixels" the actual detail does not obey the restrictions, this is to accurately represent the information and basically how it should be received.
Step 3:
The image is now obeying the restrictions of the pixels, each pixel that from Step 2 that contained X% one colour and X% another is now those percentages put together.
This is perhaps the best way to sum up anti aliasing.
Step 4:
Cutting down on the colour count, there's no reason to have dozens of colours that are essentially the same.
This isn't the work process for anti aliasing, and the final product isn't ideal. This is just roughly how you should be thinking while anti aliasing.
It's not quite as simple as "adding buffer pixels" you need to know how many, what intervals the ramps may be at, etc, hopefully this has helped with that. 
You may also want to reconsider the shading on his arms, there isn't much of that in the Venture Bros and what's there is usually part of the character design (Brock's eyes etc,) however- this is your sprite and you should really run with whatever changes you'd like to make; but try to keep it consistent as there's no other shading to speak of at the moment.
Keep up the good work.
