Okay! So, these are called proportions. I have gotten this question a lot.
So, it's all about measuring! How many "eyes" long and wide are your character's face? How many "heads" tall is your character? I follow these proportions, sometimes tweaking them:
CHILDREN (both genders: 4 heads tall.)
TEENAGERS (girls: 5 heads tall, boys: 5 1/2 heads tall)
ADULTS (6 heads tall for both genders)
I do edit these. For example, a character may be a preteen, so I do a 4 1/2 heads tall. Sometimes boys are shorter than girls or girls the same height. It really depends on the height of the general characters you draw. Here are some more tips:
-The neck to bottom of the chest region is one head.
-Legs ca be anywhere from 2 heads to 3 heads, or even longer!
-Torsos are one head, unless you want to do 2.
As for side views and angled views: these can be hard to get right. I would not suggest you try them until you have the front view mastered. But, like I said, measure. Do turnabouts, even consider making character sheets with different views. Find styles you like for side views and angled views and use those! My side views are more detailed, as I define the nose and lips unlike art styles like SAO and Assassination Classroom, which usually drawn within the side outline.
Hope this helped!