Some mistakes I see a lot of people make, and have even made myself, are super common, but also very serious as they get in the way of your manifestation.
1. Spreading yourself thin.
With visual aids, it's good to have them around constantly. Always sort of feeding those images into your brain. It heavily influences your subconscious. However with meditation, writing, and other methods, sometimes people force it every day. They are distracted, not in the right mental state, not giving it 100% of their energy. Forcing yourself to write in a notebook for 2 minutes every day while you're thinking about other things and maybe even in a negative headspace will not get you anywhere!
It is OK if you cannot manifest every day. It's better to do it when you feel focused and positive. I find that meditating regularly and practicing gratitude helps me to be more positive and focused on a desired task generally! Manifestation is all about directing your energy somewhere, so don't do it unless you can give it your all.2. Not letting go.
This one is probably the most serious one. Manifesting is about having total trust and faith in the universe. That it will deliver. It already has! Constantly worrying, doubting, and stressing, will not help. You manifest, you put it out there with great focus and energy, and the universe is already doing its magic. Let go! focus on yourself, don't stress about doubts. If all you're thinking about is failing, manifesting not working, your own flaws... well then that's all your gonna get! because that's all you're putting your energy towards. You must have trust in the universe.
3. Being negative.
Like i've stated many times, it's all about what you're putting out. If you want positive things in your life, you have to actually be a positive person. Trying to manifest positive things in your life while also being a negative person will not work! Manifesting is intertwined with karma. If you are a mean, bad person, like a bully or something, you're vibrating on a lower level. But now you want to manifest something good? like a career, some cash, or some luck. Well that's going to be very hard, because all those things are vibrating at a very high level, they will not stoop down to you just because you have asked. You must get yourself on a positive plane alongside your wishes, so that you can receive them with ease.