An H1 average is quite difficult to manage (my average is way below an H1 - Over my 4 years at uni I've only gotten two H1s, but also a 77, 78 and a 79). One of my friends almost always gets H1's though, so it's hard to tell.
During your first two years, you will be able to get decent marks, but third year (in my case) is a completely different story. One of my friends managed an H1 average by doing third year over two years. I'm doing a similar thing over my masters year this year, since I failed a subject last semester and only scored a 65 and a 56 in another two (I did manage to get a 71, 74, 77 and 80 as well). This year I'm hoping for high 70's in all the subjects I do, and hopefully >70 in my thesis. In semester 1 2014, I would like to manage an H1 in both subjects, since there's no exam.
In order to be accepted into PhD, you need >75 (my supervisor said an H1 is really required). I've sort of given up on a PhD, I just want to finish my masters with a reasonably good score.