As for mapmaking, like I said, go for a program that let's you place things. Maptools is usually good for this since you can find images all over the net to serve as backdrops. I recommend making several maps to start out with that you can re-use, like 4-6 blank dungeon rooms. You can then take these and piece them together to make a dungeon map.
Encounter planning is relatively easy really. In my mind, 70% of the dungeon 'rooms' should have an encounter of some type even if it's something small like a minor trap or a puzzle and the other 30% can be those random rooms, secret rooms or treasure troves. Calculating CRs is covered in the DMG, so I'd recommend reading that section quite carefully. Most of the time it's pretty straight forward, other times it's DM's intuition. I always ask myself "Now...what chance do they have of surviving this?" and go from there. I always start my games with a range of different battles to see what kinds of threats the party can handle and what they have trouble with, that way I can easily more effectively provide a good challenge but wont slaughter them in the process. Otherwise doc gave some good examples in his post, just kind of give everyone something to do.
NPCs are easy as well, I usually just use the NPC classes in the DMG or I use full classes for major NPCs. The difficult part is making the character interesting, which all you really need to do is figure out two things: the npc's personality and why they would want to interact with them, cause otherwise they wont. Most of the time those NPCs have something the party wants whether that be information, and item, or something else that they would be seeking.