The best thing to do when you're trying to pick up a new style is to keep practicing, even if at first your drawings don't come out exactly as you want them to or very far from what you want. You need to keep it up.
Some of the older drawing styles for anime are more difficult than modern anime, the lines are more varied and curve a lot. A lot of people claim that it's 'more simple' because it looks more cartoonish than some modern anime. A lot of modern anime can be said to be more simple when it comes to style (not animation) due to simple fact that lines are more rigid and universal.
Retro anime however has a very wide range of lines and faces and a whole different set of proportions, so when put side by side drawing a more 'retro' style is more difficult than a more 'modern' style.
But this shouldn't deter anyone from drawing it!
The key is to be mindful of proportions and where things go (the eyes in proportion to the nose and mouth based on age and assumed gender). There is also eye shape to consider.
The best thing to do is just do some copy-cat drawings (this is not tracing) by looking at a manga panel or an anime screen shot and drawing what you see. Do that over and over again and then try drawing it on your own without looking at something. By doing copy-cat drawings you will train your mind and hand-eye coordination to follow a new type of drawing style, you'll be familiarized with Tezuka's drawing style.
Tezuka loved to exaggerate body proportions (such as noses!
) and he had fun with their shapes; rounded and bulbous, hooked and pointy etc. So you can have fun with just being creative and exaggerating body parts and faces.
There are also How to Draw Manga books out there that feature Atom, Tetsuwan Penguin bought one for $.99, that could be of great help.
Hope this all helps, I could upload a better tutorial but I really don't feel like drawing now.
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