1.
Good grades, at least 2:1, but better to be 1st; and degree level MEng > BEng, but not by far.
2.
Genuine passion for Engineering (proven by any extracurricular activities or hobbies).
3.
Work experience. Any work experience before graduation is great, but an industry relevant experience is much better. You should seriously consider doing an internship before you graduate (or straight after you graduate if you can't find a graduate level job).
4.
You ability to sell your skills during the hiring process (CV, phone & video interviews, in person interviews).