For me, if I had to give one tip, it would be: have a camera which you feel comfortable carrying everywhere. Period. This advice doesn't suit all types of photography, but it suits what I do. Probably 75% of what you see on this site happened while I was on my way to do some errand, or in the old days, on my way to work. Whether this is a Leica or an Elan 7 -- you should be able to go about your business and have a camera with one or two lenses with you.
As far as the camera equipment goes, it took me a long time to learn this about myself, but my style, such as it is, is all over the place. It might be a guy singing in the subway, and it might be a leaf on a ledge. With the caveat that your style changes through the years, right now, the SLR, because it is a system, works best for me.
I never liked the idea of having one camera for this, and another for that. The reason relates to what I opened this discussion with, i.e. you go out and you don't know what is going to catch your eye. The second reason is that it takes a while to get the feel of whatever camera you are using, and when you switch from one system to the other, I tend to get confused, or lose the feel of the equipment.
And, as much as I might deny it, there's no doubt that I like a camera that has some things to fool around with. With the Elan, I normally have focus lock set to the back button and just one center focal point -- which is essentially similar to a manual focus camera where you can focus and leave it there.
But there are times when I will set focus lock back to the main shutter button, or use all the focal points for shooting.
And though it is rare for me to do flash photography, it is nice to have a high-end dedicated flash when you want it without having to switch to another camera system and to get to know that flash as you did the camera.
All in all -- I guess I'm saying that I've been very happy with this system. I imagine that I might have done as well with a Nikon system -- but that part may just have to do with what you started with, and very early on I used the AE1 and that was that. That's just like, some people like Fords and some like Chevys.
The same instructions go for film: in general, once you find it -- never let it go. I look back over negatives and I can immediately recognize the HP5 in HC110. That is what has worked best for me as a general film. The film to have in the camera when you have no idea ahead of time what you'll be shooting.