I decided to make small list of missions that could be suitable for a beginner - person, who haven't tried TDM. It's similar to Thief missions, but some aspects (like lockpicking or fighting) are different. I really recommend to begin with Training mission and then New Job.
The order here reflects order in which you may play those missions: start with the Training mission first, then going to New Job and Thief's Den 1 and similar small and simple missions. After that, there are some more complex, but still newcomer-friendly missions (from Full Moon Fever to Tears of St. Lucia and then to Chronicles of Skulduggery 0).
But the order is not set in stone, it's just mere suggestion. You can change the order, add or exclude missions etc. Can't say that it's complete or convincing list. As I said it's just the suggestion and in any case you can ask for help (and for others' suggestions) here: https://forums.thedarkmod.com/index.php?/forum/57-fan-mis...