Can you draw realistically? If not, then you should probably start somewhere other than manga and/or anime. That's not what you want to hear, but I've seen several talented artists damaged or waylaid in their learning by focusing on a specific style to the exclusion of learning more general skills.
You probably shouldn't start with how to draw manga books. There are plenty of anatomy books you can find in art shops, and these will teach you how to draw things in realistic proportion. Someone once told me that you need to learn the rules before you break them; although I'm a writer, that seems to hold true for art as much as for literature. If you learn how to draw things in manga proportions, which are often 5-6 heads for an adult body as opposed to the more realistic 7-9 heads, then you'll have trouble learning why and how things are altered in particular styles such as manga and the effect of those alterations.
Sorry to sound like a drony art teacher, but that's the gospel truth. Draw realism. Print out pictures of naked people. Attend life drawing classes. Get your partner/spouse/friends/parents/grandparents/siblings to strip naked and draw them. Buy anatomy textbooks for art students (medical ones won't tell you what you want to know ) and sketch the human form from every possible angle. That way, you'll develop a sense of how the human body should look.
As for perspective, that's a fairly important but fortunately simple part of art to learn. Dozens of places online can teach you about 1-3 point perspective; for 4 and 5-point (curvilinear) perspective you might need to find specialist sources or check out some art/technical drawing classes near where you live.
I hope I helped.