What you going through is perfectly normal, at the beginning the body need to setup itself to yoyoing even something that seems easy as a trapeze is hard, in one year time you will not even think about a trapeze (for example).
When you practice just stop one second and think, when you miss the string for example try to slide the finger on the string and see how is happening, most of the time at the beginning is because your hands are not alligned properly caused by inexperience, slowly you will start to get in the right position automatically.
Do not despair and keep going, some stuff sometimes happen randomly, when I learnt the brent stole years ago, I was grinding all day before without success, the day after I woke up, just did a random one before go to school and I did it first try and from there I knew the brent stole.
Is all about time and keep practicing, it can be frustrating but it will pay off in the long run giving you freedom to perform everything you want.
About practice yoyo effectively, is to be without distraction (like your phone for example) and be in the moment, think about what you performing and while you do it stay focused, setup your mind on the fact that the yoyo is already on that string, it is weird but while I perform a combo I also think about “the next step”, I know where the yoyo have to land and I think about it just a fraction before perform it but it give me enough “safety” to actually do it.
In the case of basic tricks like the trapeze just think to put the yoyo on the string, move your body as fluid as you can, the missed trapeze is usually because arms and hands are misalligned and too stiff, when I teach some of my friends for fun I see where the mistake was and usually it was keeping the hands and arms soooo stiff cause insecurity of what they were doing.
Also take your time, do not watch at other progressions, everyone has it’s own path, so do not worry where you at, just take at least an hour outside the world and think about what you doing, you will see the results coming for sure