1) Not focusing on every shot on every hole. This leads to bad shots that I don't need
2) Not fueling up with food and water when needed to prevent me making a mess of shots and holes cos I am hungry and dehydrated
Get a reasonably repeatable swing then go out and get fit for clubs.
Unless you have plenty of money to burn...…… Great advice from @ChetlovesMer
My 1st 2 years, I put a set together from the local goodwill type stores. Cost me about $60.00 Once I decided to continue, I went to a local golf specialty store and tried out about 10 different sets of used clubs that some one had treaded in. Fount the set that "felt" the best to my swing and picked them up for about $200.00.
Used the cheapest ball I could find at Wall mart, until I stopped losing so many...….
Played the used set for about 3 years before I invested in a new tech fitted set.
Still not sure how "reasonable" my swing is...…… LOL