One of the best methods I have found that has worked well for me, is Zone focusing. I always aim to use a Manual focus lens with Hyperfocal Markings on it(However, it doesn't have to have these markings and a 50mm f/1.8 will work just as well).

These provide the distance of the DOF within a given Aperture size based on how far the focusing distance is and all items that can be brought into an acceptable focus.

As a rule, I carry 2 camera bodies with 2 lenses of different focal lengths. One with a 70-200 zoom that I tend to use when most people are stationery, IE sitting down for dinner or the stage, giving speeches ETC and the other, a manual lens that I use when mingling amongst people.

The discipline I have to have, is to ensure that I take all closeup pictures with the manual focus lens, from my pre-determined distance. this is the distance where my camera has been pre-focused at. The aperture then is the key, as the smaller the Aperture, the greater the DOF and the greater possibility of ensuring that the Moments have been captured at the optimal speed.

Taking into account that most clients are not overly fussed about the Noise Levels, but are more interested in the Moment, I find it liberating that I can crank up the ISO to 3200 and not have to worry about the Noise. Also, most events Photos get uploaded to archive galleries where the photos generally have to be a fairly small size to be viewed by 200/300 staff the following Monday, Noise becomes even less significant.

If the event happens to be a Wedding, the same rules apply, static moments I capture RAW/Full Frame but a lot of the candid stuff is once again taken with the means of Zone Focusing as you never know what you may catch.

The down side to Zone focusing; it produces the sharpest results at smaller Apertures I.E f/11 where a greater distance will be in focus compared to f/5.6 and less chance of misjudging your focusing distance, but this does mean; it can get extremely challenging in low light, specially for a newbie who is not experienced at this type of photography.

I was taught this technique years ago as a street photographer and my advise would be to do the same. learn your focal lengths, ranges and ISO combinations and see what gives you the best result, and then go for it!

The Canon 600D + EF50mm f/1.8 is a good combo to experiment with