In the "you can't run until you learn how to crawl" department, learning how to "dabble" in hand lettering first if you don't also gain experience in or already possess some knowledge of letter construction, good layout, how to draw letters, pull smooth strokes with a lettering brush, sharply and squarely finish the corners of those strokes, etc. will be pretty difficult.
Shortcutting those crucial parts of the learning process will increase your frustration and test your patience about the end results of your efforts.
There are some good resources here:
Sign Painting books
The Mike Stevens book Mastering Layout is a must buy. It won't help in the very beginning of learning how to pull smooth, consistent vertical, horizontal, angled, circular, curved strokes, but its a great resource for how to design better looking signs no matter how you produce them. The only real way one becomes proficient at hand lettering beyond "dabbling and dabbing" is more hours of practice than most are prepared to invest.
The next part will be the most important lesson you can ever learn for hand lettering.
Get yourself set up with a good work table, easel, etc. with an adjustable tilt if possible and a smooth edge along the bottom. After that, get a roll of white butcher paper, some yardsticks, One Shot Poster Color-Black, turpentine, a couple of GREY squirrel hair quills, liners and flats and a mahl stick. Water based paint on uncoated paper will pucker when lettered on and not provide the right drag which keeps your brush in its chiselled shape as you pull a stroke. To practice your letter strokes, tape a long piece of the butcher paper on the table, then make some marks about 2-3" apart down the entire height of the sheet on one end of the paper with a pencil. Starting at the bottom while holding the yardstick/ruler in one hand with the flat part of your index finger pushed against the bottom edge of the work bench, the other hand holds a pencil flat against the top of the ruler and paper at one of your marks. Now starting pulling your hands across the workbench as evenly as you can while drawing a parallel line across the entire length of the sheet. Repeat this until you have all your lines drawn. Take a #2 pencil and a triangle and start drawing single vertical lines spaced a few inches apart the same height as your lines are spaced across the entire sheet. The next two lines down, draw a series of horizontal lines, same spacing and length. Next line, 45 degree angled lines same routine. Next line, reverse the angle the other way. Next line, draw a the left half of a circle, then the right half, etc.... Fill up the whole sheet trying to draw the lines as evenly and as straight or consistently curved as possible with equal spacing between them.
Now mix up some of the poster color into a doubled up, unwaxed Dixie cup or small container that you can comfortably hold in your opposite hand than you will letter with. Make the paint pretty thin, but not too thin so that it runs. It takes practice getting it just right. Make a circle with your thumb for the paint cup to sit in. Between your index finger and middle finger slide a piece of postcard or index card to "palette" your brush with. Between your middle finger and ring finger, the end of your mahl stick rests. A dowel rod about 3' long will do and make a small ball of tape around the end that will rest against your work surface. Lightly hold your lettering brush between your thumb and index finger just behind the ferrule. As you gain proficiency you will be able to spin it smoothly and predictably. Dip the tip of the brush into the paint without going so far as to get paint on the ferrule. Only the hairs should get paint on them. Now smooth the brush back and forth on the index card until you see a nice sharp, chiselled edge. Go to your paper and starting at one end of one line, place the tip of the mahl stick a comfortable distance ahead of where you are stroking with your lettering hand midway on the shaft and the shaft parallel to your line of strokes. Starting above the top line, psuh your chiselled brush against the paper and pull the mahl stick down with your other hand as you try to pull as smooth and even thickness line along the pencil line. Don't worry about anything but developing a feel for what you are doing.
Do a much as you can and keep your work in front of you at eye level. After so many of these sheets, you'll start seeing improvement and then you can start drawing letters instead of just the strokes that make up letters. Then you can play around with words, different typefaces, etc. Work on a bold block typeface, a roman seriffed, and eventually a script. don't go overboard with trying to do too much until you gain some competence and confidence.
With only 39 years of hand lettering experience under my belt coming from one of the best, most intensive, trade school and union shop work/learn experiences, I've seen plenty of dabblers and shortcutters over the years and they nearly all ended up eventually giving up and doing something else. I've also seen plenty of determined folks with very little "artistic" talent stick to it and become very good sign craftspeople. I still love to letter and do so even just for fun.
A bunch of us have a group on Facebook named the Sign Painting Support Group Alternative (long story on the title and history on the group). Most people share photos of jobs, offer advice, build friendships, ask questions, get advice, joke around, etc. and nobody attacks or insults anybody.