if your predicted grades that your apply with are lower than a grade below the entry requirements for a course (and you don't fit contextuals), it's likely you will be rejected, especially to institutions that are already highly subscribed to. it's alright to put one aspirational choice down (e.g. two grades higher than predicted), but only applying to places that request higher than what you're predicted is, most likely, going to result in some rejections.
if you write your personal statement as too broad and not specific to you and your own experiences, that may also prompt a rejection. personal statements are about you, not the subject (i've read ones where they speak about how great the subject they applied to was, but not how their experiences can show that).
applying to multiple courses with no relation to one another (e.g. biology and english) is once again going to make your personal statement too vague and not specific so you may risk rejection doing this as it appears that you aren't sure what you want to be applying for. applying for multiple courses within the same institution can sometimes get you rejected for the same reason.
all in all, the ucas application is about demonstrating why you are a good fit for the institutions you're applying to and how the things you have experienced can show that! you want to sell yourself to them and your passion for your subject - you are not selling the subject to them. show yourself off but don't exaggerate!!