I have had my Prusa i3 printers for almost a year. I have the Prusa i3 Mendal and the Prusa i3 Omni. Along the way I have learned a great deal of things from building the original kits, trouble shooting, learning the programs and how to solve all the little annoyances that come with being a first time (newbie) user.
I have read countless forums, watched numerous videos and looked into the plethora of new innovations in the 3D printing world.
We all had to start somewhere and hopefully this helps anyone who is still learning or even helps the ones who have being doing this for years.

Step 1: Heated Bed - Leveling

I have glass for the heated bed. I just bought a picture frame from a thrift store and cut it to fit the bed. It is held on with small binder clips. Then I take the wire off so it doesn't catch on anything.
First I home all. This puts the extruder down to its lowest point (obviously). If there is a large gap between the extruder and bed or if the extruder pushes down too far on the bed, first you may want to make an adjustment to the stop switch (pic 7). Just the 2 screws can allow for a half inch up or down. Re Home to make sure it's close to the bed (within a couple millimeters).
Adjusting the bed level is as easy as turning the thumb screws. I use a piece of card stock I have sitting around. You might be able to use an index card. I have found this to be better than regular paper.
Start off with the four corners. When adjusting you want the card stock to have a little resistance to tugging and pushing. After the 4 corners then it'll be sets of 3 down each side. 3 down the left (top, middle, bottom), 3 across the bottom (left corner, middle, right corner) and so on.

Step 2: Making Your Print Stick With ABS Slurry

I have read and tried many different ways to make prints stick. Using masking/painters tape, hairspray, ABS juice and my slurry. Using the tape has been problematic because the print sticks to the tape (almost a permanent bond). Hairspray, if you get the right kind (ultra hold) does well but you have to clean the glass so often and it's just too time consuming for me. ABS juice is ok as long as you can find it or mix it up to exact specs...but the slurry has never let me down.
I start with an empty pickle jar (or whatever jar you have handy that can seal up). I start with half filled with Acetone and add scraps of ABS (recycling my many mess ups!). After awhile the plastic dissolves in the Acetone and I just keep adding more. I use the popsicle stick to stir it up and smash down the ABS. Keep adding a bit of each til you get a pancake batter consistency or like Elmer's glue.
I preheat the printer for ABS. Once it gets to 60°C I then use the popsicle stick to glob some slurry onto the bed. I then use a putty knife (paint scraper) to smooth out the mixture. About the thickness of paper.
I use Cura for my slicing software. As you can see from the first pic, there are a bunch of squares. Each square is 10x10 mm, so you can smear the slurry on the whole bed or just where you needed it.
Cleanup is a breeze. I use the razor to clean off the putty knife. When the print is done it'll just pull off the bed. If it cooled down then preheat again and it'll peel off with no probs (worse case scenario you will need to use the razor to scrape off the slurry, but I never have needed to).
Won't lie, I have never reused the slurry to make more slurry. It might work, I don't know (Haven't tried).
The slurry also works for welding pieces together. I make large props, so a quick swipe of slurry and hold it for a couple seconds is all it takes.

Step 3: ABS Printing Set Up

Here I have many different prints in various stages. Using the slurry has eliminated any and all peeling from the bed, and eliminated the need for brims or rafts. This will cut time from printing and since the slurry is paper thick, it peels off the print and eliminating most need to use a razor to clean up the base.
Layer height can vary between .06 for fine prints (longer print time) to .3 for quick prints (shorter time but less details).
Shell thickness I have always left at .8
Fill bottom/top is .8 and fill density I usually run between 20 and 35%.
With the slurry I have been able to print in sharp angle (almost vertical!) but if their are under cuts then you definitely want the supports added.
If you look at pics 7 and 8 then you can see the difference between .1 and .3 in layer height. At .1 you can see even and smooth lines while .3 has some gaps and aren't as smooth. Not a big deal because in the finish you can fix this.

Step 4: Printing Your Own Parts

So this is where Thingiverse has been extremely useful!
All of these machines don't usually come with the really useful stuff. Well, I mean it's all useful, but these make adjustments a lot easier.
Thumb screw make leveling the bed easier (and you don't have the butterfly ends catching on the frame).
Spool holder so it doesn't get caught up or fall off the table and go rolling across the floor.
Pics 5 through 9 are belt tensioners. Mine didn't come with any way to tighten the belt. After awhile the belt wore down and stretched but there was no way to tighten it with taking it apart again.
I updated the springs for the bed. They are longer and thicker. Once they wear out the bed just sags in that one corner and makes it almost impossible to level correctly.
I printed a new motor mount so the bed limit switch was no longer attached to the bed. It kept pulling out the wires and I was tired of replacing them or resoldering them.
The wires for the bed kept getting caught underneath and catching on the frame. So, I took one of the clips and ran the wires through to keep them from bunching up again.

Step 5: Finishing

As I said, using the slurry makes this part a bit easier. Just peel it off the bed and then peel the slurry off the print. Pretty simple.
I use the Glazing and Spot putty because it just smears on and easily sands down. Dries quickly too.
Most of the stuff I just picked up at the hardware store or Auto parts store.
Pricing- I went with the Prusa i3 because it was cheap. Found on eBay for 170 for the kit. Shipping wasn't to bad, so it was still cheaper than everything else I saw.
ABS filament I get for 12 to 15 bucks for 1.75 mm. So it's cheap to run.

Hope these help people! Probably known to quite a few but it never hurts to put it out there for anyone curious enough to want to try for themselves.
Feel free to add more tips for 3d printers in the comments! I may have forgotten some, and I'm always open to new things to try!
Thank you!