I kind of misuse dA's features, and it's come to my attention recently that some of this can be interpreted as fishing for pageviews, which I would like to clarify IS NOT MY INTENTION AT ALL. I don't really care about them, I'm not active enough on here to ever expect them to be at all high, so as a result I mostly just don't notice them.

ANYWAY.
1. +watching. I generally don't, unless I know you from elsewhere. I treat it mostly like a friendslist - however, I will occasionally +watch someone I don't know if I'm in a weird mood. I don't really like the system; I prefer to go through a person's gallery in one sitting, rather than just get alerts on changes. I'm also uncomfortable with +watching strangers because it seems kind of creepy to me. I know -I- get a little weirded out when random people I've never heard of +watch me. Instead, if I like someone's work, I will....

2. +fav. I treat my favorites as something like my watchlist. I keep it on 'random' on my profile simply because whenever I visit my profile page, I will usually click at least /one/ of the favorites that come up, then go through the artists' entire gallery. So basically a +fav from me is equivalent to a +watch, and it usually means I've gone through your entire gallery (or the first 5 pages if it's unreasonably crowded) and I intend to go through it again the next time your picture comes up which is fairly often (seriously, more so than you'd think). I figure this system is, overall, preferable to you, since while no one but you and I will know I +watched you, but a +fav has the chance to be seen by anyone who stumbles across my gallery. For this reason I tend to only +fav one or two pictures by someone, at least in one sitting.
(tutorials are a special case, bee tee dubs; I tend to +fav/collect any decent tuts I come across because my personal philosophy is that they should be spread as much as possible through the internets. Friends' works are also generally exempt from the '1 or 2 per person' rule.)

3. Commenting. For the most part I don't, unless I have something particularly insightful to say. I wish I was better at writing good comments, but I'm not, and since I hate insincere/banal comments ("it's so cute : D") I tend to avoid them on the whole. If you get a comment from me feel special :0 Note that this also applies to replying to comments - this I honestly feel very bad about, but I really am uncomfortable replying to them. I read them and I <3 you very much for making them but whenever I click the reply button my brain freezes D:

Oh, by the way, the likelyhood of me +faving something of yours is, roughly, inversely proportional to how many comments/+favs it has already recieved. Mostly I don't +fav anything with over 1000 +favs unless it really speaks to me personally or something like that. I'm more strict with this now than I used to be.

So there. I hope that was informative. :0