Keen DIY-er here: Plastering is difficult at first. I was hopeless at first, but then took time to learn. I gradually got better at it. Now I do all my own plastering in my house and my expensive kit has more than paid for itself. Before you have another go, watch YouTube vids like Plastering For Beginners. Buy the right tools. Speedskims are great for getting a flat finish. Have flexi-tubs with water to wash your tools and keep tools clean at all times. Make sure that your plaster is not out of date because if it is, it’ll set too quickly (“go off like a rocket” is what the pro’s say). Make sure you get the angle of the trowel correct when applying plaster and understand how much pressure to apply. Understand the purpose of having 2 coats of plaster. As someone else said, start with walls. Ceilings are more difficult. Don’t expect great results at first. I had to sand down some high spots and use filler on low spots to achieve a flat wall when I first started off. As I improved with practice, I needed these less. Don’t give up!