there are different tricks to cover out your lack of backgroundness.
1) ink the background pitch black.
2) use a lot of speedlines.
3) use CG patterns for background.
4) use word bubbles (huge bubbles) to cover the background.
5) simply just trace a background from a photo.
6) ask an assistant to draw them for you.
Backgrounds aren't something that need to be drawn in every single panel, thankfully. You should take reference from other manga to see how they handle backgrounds. You'll find everything Queen had mentioned being utilized and it's easier to think of how to do it when you see it. Much luck.
I really don't recommend tracing photos for backgrounds. It often looks jarring. Doubly so when the person tracing the photo has a poor sense of perspective so the characters aren't drawn into the background as well as they could be. It also can look weird if your style is not realistic and then you toss your characters into a totally realistic background.
Well, if you're not familiar with perspective, you should look that up. http://sashas.deviantart.com/art/The-Perspective-Tutorial-94166651 At first it can feel really tedious to measure things out. I don't know many people who like drawing grids and stuff (minus one teacher who had the motto "Perspective is FUN!" ), but with enough practice, you can know where things go by eye more often and how to mess with perspective and have it look like you totally did it on purpose.
I know of some people who build the recurring places in their comics using Google Sketch-up and one who just straight-up builds dioramas.
It's tempting as hell to never draw backgrounds... but if you resist temptation often enough, you can probably figure out how to draw backgrounds that don't suck eventually.... eventually. oTL backgrounds are hard...
Research and reference is the most important thing. Try making a schematic and prop sheet - you can do a flat, overhead view using just boxes and other shapes to mark where things go, and/or draw sketches in perspective. This is really messy because it was for my personal use but here is an example.
A tip: MURDER THEM WITH RUSTY SPOONS. THE LOT OF THEM. scream
1) ink the background pitch black.
Question, what if there's a lot of black on the characters? I've been trying to use white highlights to separate, but it ends up looking stupid?emotion_8c
I wish I had a background assistant. I think my brother-in-law offered... hm... ninja
That's a way to do it. Sometimes it looks better to just let parts of the character blend in to the background. Look at how others do it. Western comics may be better to study for this even if you want to draw manga, simply because there seems to be more black placement in them. Alex Toth is an artist that comes to mind.
The background is CRUCIAL to a good comic. Always imagine the scenery as another living, breathing character. They help you create a believable world, a world that makes us want to live in it (or not). This world is your setting, and it establishes the rules to your reader, and how your characters are affected by it, and may want to change it. For example, if it's a post-apocalypse, or a dictatorship, then you need to constantly show us how this world has turned to crap, and how the landscape has changed according to that.
Backdrops also help readers follow your characters through the use of an establishing panel shot, and location tagging. Establishing shots set up the location, props, and where all characters are within it. When blocking your characters in following panels, you want to use backdrop props to help us follow where they are moving from and to, in conjunction to other characters (this is location tagging)... so we'll know if a character has moved away from a desk, out the door relative to that desk, and down a stairwell relative to that door.
Research is a very good thing to put effort to! In creating your environments, I always gather references... from the internet, books (other comics, concept art books, architecture and geographical/cultural books), screencaps/videos from movies or video games, etc. You want to think about time period, location, genre, etc... and narrow down and pull in influences and inspirations from other sources to merge together in creating your own world.
In drawing it out, when you figure out where you want your characters in a panel, you can do a quick sketch composition of where things go in a backdrop, before you apply any sort of correct perspective. Just remember to leave enough backdrop for environment and word balloons (which is also something you should imagine as a "character" to properly compose within panels).
A lot of serialized manga backgrounds are traced, so if that's the look you are going for that might be something to try out.
A lot of artists are doing that now, but it's pretty obvious when they do (but at least it's not as bad as that god-awful photo with a filter slapped on they were all doing a couple years ago). One still has to understand perspective in order to place the character right so it isn't so conspicuous. In the end it is also very limiting - more dynamic angles will be hard to achieve and the background objects will be limited to what exists in real life. I think a lot of artists are doing this because of deadline issues rather than a deficit in their drawing abilities. Being able to construct your own backgrounds ultimately makes your work more successful because you have more power over what goes in to each panel.