Candy journal - keep track of temperature, consistency, ingredient tweaks, favorite ingredient types and brands, and general candy history.
Batch weight - use a kitchen scale to weigh your candy after it has turned, this will tell you how much chocolate you need to cover the fondant when dipping. You will need the same weight in chocolate as the weight of your batch, e.g. if your batch of fudge weighs 4 lbs, you will need approximately 4 lbs of chocolate. For proper dipping you will need to use 3-5 lbs of chocolate as a base. You can reuse this chocolate as long as it is kept clean and properly stored.
Temperature - a good thermometer and correct temperature for your elevation are imperative. Find your exact elevation, (grab an elevation finder app for your phone) then use this chart (chart coming soon) to find the appropriate temperature for the type of candy you are creating. Journal your temps and consistencies to fine tune the recipes for your location. You will find many different charts online for candy making temps, this is the chart I follow, but you will want to make adjustments for your area, and keep track of what works best for you. For every 1,000 feet elevation above sea level, decrease the temperature in the recipe by 2˚F.
Don't scrape your pan - resist the temptation to scrape the candy off the side of your pan while pouring onto the slab. Scraping the pan greatly increases the chances of your batch turning to sugar. All is not lost if your batch does turn, I teach how to save your fondant in my centers classes.
Slab size - 18x22 is my favorite size for a marble slab. It is easy to move and fits in most sinks for cleaning. You can often pick one up for a discount from a stone countertop company. Marble is the best surface for cooling and turning candy. People often ask if they could use granite, quartz or a composite, but they are too porous, can crack with heat, and/or don't hold the chill as well.
Marble slab cheat - If you don't have a marble slab, cool a 9x13 or larger pyrex casserole dish in the fridge.