I've always just let teachers know that I'm happy to supply them with a resume, copies of my essays, or anything else that they might find helpful in writing their recs (some have taken me up on it, some haven't, but I like to put the option out there). I also generally say that if it would be helpful, I'm happy to meet and talk a little bit about my goals and interests. Whatever, just to make it clear that I'm open to their questions, I'm not just handing them an envelope and washing my hands of the situation.
My high school told us that three weeks should be the minimum time between a request and a deadline, but obviously longer is better. Also, check in once or twice (depending on how long of a time span it is and what their response is after checking in once) to remind them about impending deadlines.
Waive your right to see the recommendation. I'm told that colleges find it a little fishy when students haven't waived the right, but even if admissions officers don't care, it's polite.
Nice thank you notes are all that's really necessary, but I also gave small gifts to my rec writers (good chocolate). It's just a judgment call...I happened to know my writers all really well and they'd also written a lot of different recs for me, not just school applications. Whatever you do, just make sure to show gratitude. I also think it's nice, though not mandatory, to let your writers know how to contact you in the future, should they be interested in knowing what you're doing (just your email or something...again, probably depends on how well you know them).
If you have any weird circumstances (i.e. stuff that would require explanation or an addendum in your explanation), I'd suggest addressing this with your rec writers, either in a personal meeting or in an addendum to them (letting them know that they're free to ask you for further details/clarification).
I've requested recs both in person and email. You don't need to worry about it...any teacher is used to the question (it can be a little more awkward with EC supervisors, coaches, etc. who may not have written them before, but you can broach the question similarly). I just stayed after class or went into office-hours or whatever and basically asked "Would you be willing to write me a recommendation for _____?" Sometimes I prefaced it with "I know it's a really busy time of year for everyone, so feel free to let me know if this won't be possible, but would you be willing to..."
You'll be fine. Remember that it's a question teachers are totally used to
