Few fundamental mistakes in Magick
Only my tradition is the real one
Nope. People of different traditions and practices can easily achieve same results. It's not even true that some traditions are better for something and worse for something else. If you find some tradition that really suits you, you will be able to do anything with it.
Only chasing enlightenment is the right path
Well, reaching enlightenment is possible only through selfless and devoted practice, I am sorry but that's not really possible if you are consciously chasing the enlightenment because that's selfish, practicing to gain the ascension is a selfish act. Not helping others because you are saving energy for you enlightenment is even more selfish. Rather than that do stuff for yourself, it will have better results in means of enlightenment than this.
Magick is based on the subconsciousness
Simply no. All worlds, whether physical, mental, emotional, astral or spiritual, are merged together. Is Magick part of the subconsciousness? Yes, same as of everything else.
Casting a circle is for the means of protection
He he, no. The circle is casted because its energy shines with a very bright light and is visible in great distances like a lighthouse.
Point of the circle is to drag attention, to say to nearby spirits and forces: "Hey, something's happening over there, come closer".
Also, the circle lifts its energy up in a tornado like manner, that can effectively destroy anything above it. Cups and dishes falling from the shelves, glass is cracking, smaller objects "disappearing". One fellow Magician e.g. reported that his favorite chinese tea cups were broken when they fell from the middle of the table while he was performing a ritual in the floor just below the table.
If you want a protection, then banish, then enclose yourself within a Magickal chain, or bubble, or whatever.
Banish before every ritual
Congratulations, you have just effectively made your ritual useless, banishing equals to no energies around, which means no spare energies for the ritual.
It's important to banish time by time to get rid of negs or whatever you call these, but banishing once or twice per month is good enough.
Banish after every ritual
Take a following scenario, your friend kidnaps you from your home, threathens you to do his bidding and then tells you to piss off his house before he grabs his shotgun. That's what banishing after the ritual looks like.
To do it right, use a license to depart, where you give an allowance to leave to the nearby spirits, you also remind you of the bidding and request them not to bring any harm to you and your family. Also, don't be scared if they don't leave right away, sometimes they like to stay around for an hour or two before leaving. Use the banishing just only when the sh*t hits the fan.
I can use any practice of any tradition without the knowledge of its background
Just no, same as you cannot and should not pilot a plane without a proper training and tests, you shouldn't borrow practices from traditions you know nothing about. Same goes with the mixing, you can analyze and take the core of some practice and create new method based on the core that you will put into your custom system, but don't mix different practices from different traditions unless you want your life to become a misery.
Everything in grimoires must be done exactly as it is written
He he. Grab your grimoire and check the language it is written in and it was translated from. Chances are that these two are completely different, which means someone had to translate it for you, and trust me he could had translated it in hundres different ways, each and every sentence.
Words of power that should be kept in its original manner should be kept in the original language, which means that everything that WAS translated can be considered as "do something like this, say something like that" instead of "do this, say that".
Modifying procedures to suit your needs is also fundamental to the healthy occult practices, it helps you to develop intuition, reasoning and also understanding of the matter. But really, take grimoires only as a inspiration, not as the only possible strict procedure.