This is a broad subject. The how to place images (I'm assuming how to compose your panels?) that is.
The panel composition, SFX, and backgrounds all depend on what specific story you're trying to tell.
As a general place to start, I'd suggest you look at other comics that you admire and write down what they seem to do. Take note of what you like and figure makes for clear storytelling.
Composing the panels and images within is about more then aesthetics. It's about what tells your story clearest.
As for Line weight! This is a topic I know about
A general rule is the lines are thicker for areas that would have a shadow, need to be distinct from other things around it, or are heavier/thicker material.
Thinner lines are used for things that are more delicate, closer to the light source, or made of lighter more airy material.
This is a way to start thinking about it. A good way to practice is to just practice drawing objects around you and paying attention to how the lights and shadows fall and try to show that through line weight alone.
Also if you like any manga or comics that do line work especially well, then it would be good to study those and see how they approach linework.
Off the top of my head, the One Punch Man manga does an excellent job with their lines and would be an example of how to work with effective line weight of you're only working in black and white.
However if you're working in color, then I don't think the line work has to be too dramatic. You'll still need it if the coloring is simple, but if there is a lot of "weight" added to the figures and objects through your shading then the lines weight variety can be even more subtle.