I keep having problems with blunders and checks, captures and threats
What should I change it to
You have to check each and every move before you play it to verify it is no blunder.
First you think about your move and decide on the best move to play.
Then imagine your intended move as played and ask yourself: "what could my opponent do?"

Play as many games as possible for you. You won't improve your skills if you won't have enough experience.

You need practice. If you dont have time to play bunch of games I would recommend you Magnus trainer app, its great! There you can find all kinds of drills which will help you improve tactics, board vision, pattern recongition and much more. I dont use it anymore because I had to delete it (no memory on phone) but it helped me so much, from 1400 to 1600 and I believe that it will help you even more. For example I remember this one exercise where you had to move pieces safely to a certain square avoiding all captures from your opponent's pieces. By doing this few times a day your brain will get used to it and you will be able in your games to avoid blunders even without thinking about them.
Reccently, I have been losing a lot of games due to one move blunders. I am trying, as some people have advised, to look at my checks, captures and threats for both myself and my opponent. The thing is is that it is very hard to do this with every move. Can you advise?