There are so many awesome helping hands here! Just some things I've either learned the hard way or taught myself...or been taught!
1) Don't get overwhelmed. Even small projects can take hours of time, especially when you consider finding a pattern, looking at colors you will need, getting the colors you need, doing the pattern, then doing details and finishing. It is all worth it, but...
2) Take breaks, even if you haven't done much. If you get tired or frustrated sometimes it is better to put it down even if it's for a few minutes or, in my case, half an episode or ten minutes of a movie
3) Find an organization that suits you. There are many ways to organize projects or containers, but it's best to have an idea of what you want to do first. I currently have about 3 big containers, and 4 organizers for thread, 2 for DMC individually organized thread, and 2 for projects.
4) Start with a small project, especially to get used to different stitches like full and half cross stitches. Half cross stitches are NOT a bad thing, they are excellent for subtle details. However, there are plenty of designs with only full cross stitches. If you enjoy the small project, start something bigger and make your way up to more detailed and bigger projects.
5) Sometimes working on something with a goal in mind can be motivating. Over the years I can start Christmas projects as early as August, but Christmas is a huge motivator, especially if it is a gift. This last year was a success, everyone received their gifts to actually put on their Christmas trees! But any holiday or upcoming event like birthday or anniversary will do!