1. Trying to come up with something to say. The act of trying is an indicator of effort. Your approach needs to seem effortless and natural. Your goal is to have many ideas up your sleeves that you should have choices in what you can say.
2. Thinking about interesting things to say. When you think, you have to pause. This freeze in time makes her realize you are searching for interesting things to say. Meaning you are "planning" to impress her rather than being yourself and having her feel comfortable talking to someone genuine. Instead, you should just say whatever that is on your mind. To do that, you should have a mindset of being emotionally positive, happy and enthusiastic. Enthusiastic people always have something to say.
3. Initiating partially. If you feel strange or awkward approaching her, then she is going to feel uncomfortable being approached by you. Even if she is perfectly comfortable being approached, but being approached from a man who does not want to approach, will make her feel she needs to lead rather than follow. That is, as stated before, crash hard. Whether you are approaching, hugging, smiling, do it with confidence and do it fully. The confidence that says it is okay. Half a smile, half a hug, half an approach puts her in the leadership and decision making mode - a mode that says she has to mother you, a turn off mode.
4. Only having one topic to talk about. If you only have one topic to talk about, then the topic becomes her interest, not you. If you have multiple things to talk about, then the interest is on you. It is absolutely vital you talk about many things. Your many hobbies, interest and activities. Try new things.
5. The purpose of approaching is to see if she is worthy of you, not to pick her up. If you go with the mindset that you are approaching to pick her up, then you will feel bad if you get rejected. If you approach to see who is and how she is and whether she is worthy of your time, then you will only pick her up if she qualifies and proves herself to you.
There are, of course, other errors that can occur such as not leading, not bouncing, not showing sexual interest, but I have already talk about this in other articles.