I personally would say to not start with Joplin or the "big 3" classic composers, as their rags in general are fairly tough, in syncopation, and sometimes in texture.
Start with a ragtime instruction manual. Though there have been recent manuals by Glenn Jenks and Galen Wilkes, and you could use these if you want, I would recommend trying the Christensen, Winn, and Joplin methods first. The Christensen books (there are several editions, basically the same basic text with a few changes and additions from year to year, from the earliest ragtime manual in 1902 or 1904 to the "swing piano playing" method of the late '30's) start from the beginning teaching you to read music, and has some tips on scales, chords, and fingering. It goes right into ragtime and includes easy rags written by Axel Christensen himself, and some by associates such as David Rechstein, Marcella Henry, and Edward Mellinger.
The Edward Winn method, though not as extensive as the Christensen books, nonetheless provides some interesting and thorough coverage of such matters as a good ragtime left hand, as well as other such territory not covered in the Christensen text. It is certainly worthy of study as well.
Scott Joplin's "School of Ragtime" is an indispensable and extremely valuable look at the composer's thoughts on his own music, and ragtime in general. Though Joplin did get a bit too hifalutin at times (saying on some scores that "ragtime should never be played fast", which in my opinion is certainly true of his rags, most of the "big 3" rags, and classic ragtime in general, but certainly not of a few other rags by other composers that are specifically marked to be played fast), he did have a good grasp and a certain vision of how his music should be played... for instance, IN HIS OWN WORDS in "School of Ragtime":
"We wish to say here, that the 'Joplin ragtime' is destroyed by careless or imperfect rendering, and very often good players lose the effect entirely, by playing too fast. They are harmonized with the supposition that each note will be played as it is written, as it takes this and also the proper time divisions to complete the sense intended".
"The American School of Ragtime Piano Playing" by H.J. Beckerman is a most worthy addition to the ragtime instruction book pantheon, and in my opinion, it is the most impressive. It not only starts from the beginning with notes, scales, etc., but teaches the reader scales, and some basic classical techniques as well as providing examples of semi-classic music such as waltzes and reveries, both in original form, and "ragged". It ends with the same kind of thing as the Christensen books, the old "ragging the classics", which can also refer to popular tunes or folk songs of the day.
All of the above-mentioned manuals can be printed out free here:
http://www.ragtimepiano.ca/rags/review5.htmI should mention that most of the music included in the "Ragtime Review" magazine of Christensen's, including most of his compositions and those of teachers Ed Mellinger, Marcella Henry, and Robert Marine, can be found here... they make great beginner rags:
http://www.ragtimepiano.ca/rags/review3.htmSome more advice... most of these books only present each different exercise in one key, such as C. I recommend transposing EVERY EXCERCISE into EVERY KEY and playing them in all the keys. If it is in major, play it in all 12 major keys, if in minor, in all 12 minor keys. This will help your transposition ability and also help you distinguish chord relationships within each key.
I also strongly recommend you get the HANON excercises from Schirmer books. Again, each exercise is usually only presented in one key, so play them in all the keys. As the Wikipedia article notes, the excercises themselves are fairly tedious and unmusical, however some of them are extremely valuable since they teach you proper fingering of scales, thirds, sixths, and octaves. The Lee Sims method book I mention below has a nice excercise in consecutive fourths, with the correct fingering.
http://en.wikipedia.org/wiki/The_Virtuoso_Pianist_In_60_Exercises---
It should be noted that in addition to these manuals, there were also many novelty piano instruction books illustrating the finer points of this somewhat more complicated and varied descendant of ragtime.
Good ones include books by such great composers and performers as Zez Confrey, Billy Mayerl, Rube Bloom, and Lee Sims. In addition, I have seen or personally own copies of a set of "Vincent Lopez" piano method books, ghostwritten by someone named Jim Hill Smock, and also a very weird and experimental book by Glenn Waterman used as part of his piano teaching course in Los Angeles in the late 1920's (1927 or 28, I forget which). Ted Tjaden's site notes an earlier Waterman text from 1918, but I have not seen it. Unfortunately, all of these later manuals seem to still be under copyright, or at least were published after 1923.
I personally own Volume 3 of the Lopez/Smock series, Volume 2 of the Lee Sims Advanced piano method (which has some GREAT insights on harmony), and the aforementioned Waterman piano playing book, and will try to have a friend scan them for possible re-distribution. I will also try to find out about copyright status on these texts.
However, at least two good books will give you an overview of novelty playing... the 1920 book on "Rag and Jazz piano playing" on the Tjaden site above, and a late Christensen manual from 1936 called "Axel Christensen's instruction book for Modern Music", which gets pretty heavy into the novelty stuff about 3/4 of the way through. This latter book is available in its entirety free online here:
http://www.2multiples.com/hotdance/phpalbum/main.php?cmd=album&var1=books%2Facib/best of luck with your efforts!
