The 10 biggest things I've learned:
1) Get an excellent / cheap printer. Epson has the cheapest inks that I've found, and they print in good quality. They aren't a photo printer, but they're excellent for school work.
2) Have the $1 Store be your first stop EVERY time. I go to the dollar store almost as much as I go to the grocery store. I especially hit it in August and late December early January. Need a poster board? They sell 2 for $1. Need more stickers? Rewards? Glue? Pens? Foam letters? Fuzzy Pipe cleaners? They even have awesome preschool-3rd grade books with school work pages.
3) Invest in a laminator. I grabbed mine from Target for $30-ish. It is easy and I've only ever had one jam (and that was when my daughter was playing with it) and I've laminated close to 60 pages. I will say I was certain I would use the 4x5 pockets - I haven't used one yet, just go with the plain sized paper pockets. Not only will it save on printing, it will also allow your kids to write and wipe (with a dry erase marker), and stick things over and over. All of my calendar is laminated, it works wonders.
4) Set up a Pinterest. If you don't have one already (how have you avoided it?!) set up at least one board for each school year you homeschool. This is one of the coolest ways to get inspiration. You can find printables, crafts, science projects...etc.
5) Join Teachers Pay Teachers. This website is awesome! Its also great for all education levels. The account is free and there are tons of free projects in it (use the left hand side to narrow your search) I have honestly taken a lot of my print outs from the free section - I've only spent $8 on it and I felt it was well worth it.
6) Set up a permanent homeschooling spot - even if its at the kitchen table. You'll need storage, wall space, somewhere for projects to dry, and its best not to do it over carpet, if you have to - get an area rug. Having a space is ideal because it helps the kids know its School time and not time to play and get distracted.
7) Be flexibly disciplined. Listen to your kids, there are certain days when I just know that preschool is going to be a bear. Its during those days that I call an audible and we either do a fun project, something relaxed like a color by number, or we skip it all that day and make it up the next. You'll learn when your children have better focus. I find our best focus right after snack and lunch time and that is when paper-work should happen. Art projects can be scattered where-ever, and science *sometimes* will help settle them down.
8) Variety is the spice of life, and preschool. No one wants to do the same thing over and over and that's the truth especially with young children. That said repetition is one of the best ways to ensure something sticks. Varying how something is taught and practiced helps a lot. For example if you're teaching small, medium, and large, try it with a page, blocks, and the Leap Frog Tad movie, three different ways to encourage learning the one concept.
9) Curriculum, curriculum, curriculum. This ones the hardest and most fun for me. The planning stages. Every Sunday or Monday I plan for about 2 hours of my day. Usually I get about a weeks worth done in that time. At the beginning of the school year I planned out a rough curriculum, I pulled up a variety of Kindergarten readiness tests, and made sure the points in them were covered in our studies.
10) The biggest thing I've learned so far though is to do it. Invest time in your kids and their learning. After all - they're a huge part of you.