Remember though, if you focus your training too much on E+ specific elements, like nade/bfg movement, hardcore flicking and switchspamming, you will cripple your ability to transition into other Quake-like games. It's best to train the vq3 basics first and then add the E+ quirks into your gameplay, the foundation is much more important than what you build upon it, makes abandoning those parts of e+ gameplay you won't ever use in other games that much easier.

What you should train is, ground movement (strafe/circle jumping), positional awareness (focusing on sound cues to divine your opponent's location, it's really best to just do it online as bots are extremely predictable in their movement), solid, STEADY aiming as opposed to erratic, flicky aiming (useful here to get a fast kill, not so much when you're required to track someone with lg, for example, or place a direct rocket in someone's face), intelligent weapon switches (forget about switchspamming, it will FUCK YOU UP in the long run, as a player. Really think what weapon is the best choice in what situation, it's important even in E+. Unsurprisingly , it's probably the hardest thing to learn properly while playing E+) and map control (not prominent on E+ due to the lack/insignificance of items, but learning about and taking advantage of architecture, knowing WHERE you go and WHY, CONSCIOUSLY, is very important. Most players, even some good ones, tend to just blitz around maps, making most of their decisions on a sub-conscious level without ever thinking what they're doing. If you'll study the demos of some of the best players on E+, you'll notice that their decision making is extremely particular. This is a rather esoteric skill, it's importance somewhat played down by the pace and randomness of E+ gameplay, but it's universal and just super useful in all games).

For best effect, pick one element, focus on it, and play games against real opponents while keeping in mind what you're trying to learn. Utilize it in combat situations, because that's where your brain usually fades out in favour of instinct and adrenaline. Focus, focus, focus, practice, practice, practice. All there is to it, really, no secrets techniques, no clandestine methods. gl.

edit: Also, what Mirc said earlier about getting used to your setup and config. There is no golden middle IMO, just pick some settings which seem fine and stick with them.