It doesn’t matter if you’ve been making wine for decades or if you’re just getting started with home wine making. It is important to understand some of the common wine making problems that wine makers can run into. This way you can hopefully avoid these or know how to reverse the problem before it could potentially ruin an entire batch of homemade wine. 
One mistake that brand new home wine makers is not using quality equipment that isn’t made for wine making or isn’t made of a clean, unused food grade material. Many times first time wine makers will use old or used buckets that held other foods. This can be a mistake because the plastic can hold on to flavors that could make their way into your wine. I would suggest spending a little bit and purchase some quality wine making equipment from a reputable store or website. It’s not worth risking all the work and money you are putting towards your homemade wine.
Deciding to not make your wine according to the instructions or recipe is another common mistake for new wine makers. As with cooking it is necessary to follow the recipe to ensure a successful outcome. Of course with experience one can start to add their own tweaks and changes to a recipe but I don’t recommend doing this or trying to take shortcuts until you fully understand the wine making process and know what each step of the wine making process does.
Water quality is also a potential problem if not taken into consideration. Water that is hard and has a very high mineral level could cause your wine to not be the best it could be and the appearance of your wine might not be as clear as it could be. Personally I always buy bottle spring water for my wine batches. I figure for $.89 per gallon its cheap insurance against making a wine that isn’t the best it could be. I have hard water in my town, although I have a softener I’ve heard its best not to use water softened with a salt based water softener so I just go with the store bought spring water. Note: Never use distilled water. This water has basically zero minerals and also isn’t recommended for wine making.
One of the most important steps for making quality wine, and easiest things to screw up is ensuring all of your equipment and bottles are not only clean but sanitized as well. The definition of clean is basically free of any foreign material or residue. The definition of sanitized is: treated with chemicals or heat to eliminate or prevent the growth of organic matter such as bacteria, molds, etc. I typically use a sanitizer called “One Step”. Basically you mixed one tablespoon of One Step with a gallon cool or warm water, dissolve and use to sanitize your equipment. I’ve never had any problems with it. Here a product link if you’d like to take a look yourself: One Step
Not allowing your wine sufficient time to age or mellow out is another mistake made by new wine makers. I can speak from experience that it is extremely hard not to pop open a bottle of your homemade wine to see how your hard work has paid off. Typically wine ingredient kits will give you a minimum bottle age time to ensure your wine has had a chance to age. Although this is typically a minimum and any time you can go past this will only result in a much more mature, mellow, and tasty wine. Patience my friend!