For most abilities, using a light attack and immediately using an ability while the light attack animation is just starting will serve best. There are some people who like to weave in light or medium attacks after channeled abilities like Sweeps/Jabs but I have never seen any results from doing so. Of course, I could just be doing it wrong, and am open to being corrected on that by more experienced players.
But for the most part, LA before skill activation will increase output in most situations. It's so fast that, if done properly, you basically don't even see the LA animation. We on the PC have the advantage of scrolling combat text and so we know that it's working. Until you have it on console, assume that if you hit LA and cancel it with a skill, it went through. It's very consistent.