As a high school teacher, I am not always able to find classroom posters that are age appropriate and that I can afford. So I make my own. Am I an amazing artist? No way! I have several tricks that help me make a poster to my liking.
1. My Projector
I will either type what I want or draw it smaller (and take a picture, email it, and put it into PowerPoint for easy manipulation of size). Then using my computer projector I project the image onto poster board, butcher paper or cheap paper from IKEA, and lightly trace the image or words.
This allows me to make sure the letters are spaced properly and my lines of words don't slant up or down (if I tape my poster/paper level). I do not spend time on getting the exactly outline of letters typically, just general shape and size.
If I am working on a smaller project I use rulers to make sure things are spaced properly and straight. (I am concrete sequential.) If I am measuring anything I use metric (I think in decimals not fractions) - I am a science teacher :).
3. Graph Paper
For other small project I will use graph paper. After I do all my work in pencil, I trace over it in black sharpie, tape it to a window, tape white paper over it and trace again in pencil. This is a trick I do at home a lot, because my classroom doesn't have windows. My back door gets used as a light box quite often.
4. Good Erasers
I do all my work in pencil first and because of this I need good erasers. I love these white polymer erasers, they don't tear up the paper and remove stray marks easily. Once you color over a pencil line you can no longer erase it. If you look closely at a few of the posters in my room you can see pencil marks under pink and yellow marker ... I don't make this mistake anymore ... even though I know I am the only one who notices it.
I let my students borrow these sometimes, but I always tell them how much I love this eraser, and how it is my favorite and it keeps them from keeping it and poking holes in it with their pencils.
5. Multiple Drafts
Sometimes I use multiple sheets of paper before I end up with my finished products. I may work on graph paper and then trace it onto computer paper. I may just need a really-rough-draft to plan even before I type or use graph paper. I may do all of my multiple drafts on the same page ... wait ... what? Usually have light pencil (from tracing or measuring somehow), and then I go over it in marker, erase, and go back over it again. Go over it again? Why?
6. Go Over It Again
I know this was in #5 but this is the most important step that most people never do! When you go over your writing or drawing again it gives you the opportunity to hide all imperfections. It takes something that looks like ordinary handwriting and make it look impressive. (note the difference in Learning in the previous two photos.)