If you're parking up, it's best to leave it in the stroller parking area. Take the key out and make sure you cover the handle-bar controls and the seat with something waterproof. Be aware that CMs do sometimes tidy these areas up, so don't worry if your
ECV is not exactly where you left it - it will be around there somewhere! Do be wary about trying to walk queues, as these can often involve more walking than you might think, or the wait may end up being longer than that posted, especially if the ride has technical difficulties. If you need to do some walking, I suggest you do this around the stores instead, and use the ECV in line.
As for etiquette, I just try to behave in my wheelchair the way I would on foot. However, not everyone on foot really understands the etiquette of interacting with people on wheels. Be warned that you will probably meet a lot of morons, who think it is a good idea to throw themselves under your wheels (well, I did say they were morons!). In tight crowds, you'll want to leave a bit of stopping distance between you and the person in front. Unfortunately, somebody will sometimes see this space as a convenient way for them to cut 0.2 seconds off their journey, and leap into it, then stop

. Thankfully, the majority of Guests aren't nearly so dumb, and will try to give you the space you need. Also be aware of small children, as Disney is such a magical place that they are often too absorbed to notice you (I don't count little'uns as being among the stupid people; in fact they're often more sensible than their parents

).
Please note that none of these 'insults' were aimed at anyone in particular, and that my tongue was firmly installed in my cheek the entire time

(I know you guys all know this, but you do get some of those morons toddling over here from time to time

)
Oh, I also suggest you decorate your ECV up, because it's a lot of fun, and gets you a lot of positive attention.
