It entirely depends on the missionaries that come to your door, as far as to how deep their knowledge of the "scriptures" is. Many of these kids are fresh-faced late-teens, without too much consideration for other cultures and so they tend to stick to what they're told to do: preach their version of the gospel.
Many times they canvas entire neighborhoods simply because they have to fill up their day walking around and meeting with people. Over the course of a few years, they will eventually get around to your neighborhood again. Naturally, it's not to piss you off since the new missionaries do *not* keep track of who's said "No" in the past, but to check to see if there's anyone that didn't get a chance in the first place. It could be that someone was out to lunch for that particular year--oh well, they'll get to them a couple years down the road. Of course, if you've given out your phone number or had contacts with them in the recent past, they'll pass this information onto the proper personnel in case one or both of the missionaries transfer out of the area.
Typically they do not know much about their own religion, much less so about other tenets of Christianity. It's rare (though not entirely uncommon) for these young kids to have read the Bible in its entirety; rarer still that they've studied it alongside other reference materials. They tend to have ready-made answers to some of their proponent's tougher questions, though become flummoxed when more probing questions are asked.
The men serve two years while the women serve a year and a half. They tend to have enormous success when in communities with a mitigated access to continuing education (South America, etc.) than with other entrenched Christians (Italy, Spain). They live, eat, preach, pray and sleep together (not sharing the same bed, but they do share the same room); this is necessary since it's part of their dogma to keep an eye on each other so as the other is not tempted to be led astray. Typically, their day starts at 9AM (unless they're foreign-language speakers) and they're out the door, walking and talking with people, knocking on doors (endless doors), trying to strike up conversations with completely random people about their Church, its leaders and their scriptures. They break for lunch. Then they head back out til it's time for dinner. After dinner, if the neighborhood isn't too dangerous, they'll continue to proselytize until about 9PM or so. They have one day off per week in which they catch up on their laundry, go shopping and do something fun (no watersports, though).
There are 6 discussions and they are meant to be very general from the outset. The first three deal with God, Christ, then prophets. These three are easily digestible by prospective "members." Lesson 4 deals with sin and how Christ overcomes this; 5 introduces some nitty-gritty laws (tithing, chastity, eating/drinking); 6 is baptism. All nicely self-contained, but none going into enough detail from the start. The missionaries are naturally motivated to turn in numbers at the end of the week (usually on Sundays) in the hopes that they can present themselves as being righteous and performing their obligatory duties with the right mindset.
Anyone that has met seriously with missionaries is usually put out by the fact that up until baptism, missionaries are your best buddies and are there for you every step of the way. After that point, however, it is entirely up to the existing members to welcome you into the "fold"; if the other members don't do as good a job at this (and they usually don't), they usually stop attending services. This is the reason why most people associate their good experiences with the missionaries rather than other members of the church--all of their first, feel-good moments were with them.
Missionaries mean well but don't get your hopes up--after you're converted, they won't be visiting you anymore. And if you're not interested, don't take it personal if they don't put a giant X on their "list" to make sure to never visit you again. That list only applies to those two missionaries for that one day. Who keeps track of the "Nays"? Of course, they're only going to keep track of the "Ayes."
