Welcome to SoM!
The things I had a hard time with, personally, was meditation and grounding. I have ADHD and I'm not medicated so anything to do with focussing is kind of hard for me lmao. The things that I think are most hard for people in general is 1. Having the patience to actually sit down and study. 2. Learning and studying by yourself, a lot of people want a teacher or a mentor and, most often than not, people who could teach them don't want to do so, at least not one-on-one. The closest thing you can find to this is probably an actice coven. 3. Money, this is obviously more of a physical obstacle than anything else but, supplies for spells cost money and even though not all spells need ingriedents or tools they do enhance spellwork.
There are lots of different tyoes of "coloured" magic, the most common being black, white and grey. Now something to note is people have different ideas about what the deffinition of these types of magic are so the next couple of lines are my personal beliefs. Black magic is magic with the intent to hurt people or force something upon someone without their consent. White magic is bassically the opposite, it tends to be things that help people and it works with influencing things around a person rather than trying to control their minds or something. Grey magic is anything that's in between, something that could be considered forcing something against someones will while not hurting them is a good example. Some loves spells are, in my mind, grey magic, They aren't hurting anyone but they're trying to force a specific person to like you. (they also don't usually work but, that's besides the point)
Something you have to understand about "spells not working" is that there are generally two different reasons why a spell would not work. The first is because the spell you have chosen is fake, we call these spells trick magic or fantasy spells. They are spells that go against the laws of nature, stuff like changing your eye colour, growing wings and learning to fly, or turning into a mythical creature. It just can't be done. The second is because either the caster was inexprienced, the caster cast it incorrectly, someone else cast it for you or the caster simply didn't have enough focus, energy, intent or a mixture of all three. The best thing I can advise on this is that you just continue to practice and, like I said before, study hard.
I hope this helps you, Blessed Be!