G'day Jay,
To echo the sentiment of others: Sanitation, Temp control, and Yeast management (adequate amount, temp, oxygen) are imo the big ones to nail and you'll be on the way to good beer. It's not hard to do but there is a lot of information and it can be overwhelming depending on how deep down the rabbit hole you go, the more you hook in and brew the better you will get.
My 2c:
(Sanitation) Starsan or similar, and some sodium percarbonate are perfect for sanitation, and I like to include boiling water with pretty much everything. NB- Something must be clean before it can be sanitised, if using a plastic fermentor be mindful that anything that can cause tiny scratches (such as a scotch pad or scourer) can enable tiny places to harbour nasties.
Once something is sanitised get to using it asap, e.g. if you sanitise a fermentor be prepared to pitch your wort and yeast pretty much straight away.
(Temp control) Keep an eye out on Gumtree etc and you'll get a second hand fridge for next to (if not) nothing. A 12v fan(s) in the fridge will help to circulate the air and enable even cooling, as previously mentioned an STC or ink bird are handy and affordable temp controllers to maintain a steady temp (raspi/PID are an even more accurate method of maintaining an accurate temperature).
(Yeast health) If using kit yeast be aware that the optimum temps they say to use are at the very high end of the scale.. 24c is generally not going to produce a great American Pale ale for example, but may be acceptable in some Belgians or a saison.
There are a bunch of programs that will let you plug in the gravity of the wort you are dealing with and calculate the amount of yeast you need to use, this will get you in the ball park of what is required. Oxygen is necessary for healthy growth, there are a number of ways to aerate your wort prior to pitching the yeast- to start off with most people shake the fermentation vessel (fv), pour through a sanitised sieve, sanitised paint stirrer attached to a drill, or use an aquarium air pump with inline filter.. ultimately ending with using pure O2 and an air stone. Looking after the yeast I consider to be one of the most important factors to good beer, it's a worthwhile subject to read up on.
I'd also add keeping accurate records of your brew days, recipes, yeast handling etc are a great way to improve.. keep researching, asking questions, and having fun with it, once you nail a great beer that is on par with something you'd buy you will be well and truly hooked.
