Step 1: Find Free, Hardly Used Line Arts
You can't make adopts without line arts. There are a lot of free MS Paint line arts out there that are easy and simple to use. For some line arts though, Paint will not work, so you will have to use a more complex art program (such as GIMP, which is free).
I've also noticed that it's a lot easier if you make you're own line arts, but I mean no offense to anyone, but only make your own lines if you can draw decently. I make my own MLP lines, I'm confident in my ability to draw them decently, and people do like my line arts since they have been used by others several times. I've noticed that they do sell faster if I use my own line art for the adopt (I guess it's the style, I draw them more elegantly, I guess )
Once you earn more points, buy fairly inexpensive but high-quality "P2U" line arts. These line arts, as the name suggests, are pay to use, which means you have to pay money to their creator to use them. These line arts generally come in a packet and are higher quality 9generally) then free ones. I'd say 9/10 times these are not MS Paint friendly though.
Step 2: Designs
This is what I've learned about designs: people love stripes. And what people love even more is spots with stripes. People also seem to like blue and orange together, or pastel colors.
You personally don't have to like your own designs But you have to design for dA as a whole so more people will want to buy them. I, personally, don't like my designs. I simply can not use my own designs since I'm not a digital artist, but a poor traditional artist who really only had crayola colored pencils to work with....
Also, people seem to like "well drawn" over "well designed." This means if the design is good but the line art is crap, it is less favorable than a crappy design with a cool line art.
Also, never use gradients! Just don't, that's just wrong...
Step 3: What to Sell:
For the longest time I used to sell MLP adopts. I used my own lines, colored/designed it in MS Pain, then applied shading in GIMP. People loved them. They would all me "name your price", and I could earn 10-40 points per adopt. Considering these took about 2 mins. to make, that's a lot. Now, MLP adopts don't sell as well, but they are still pretty popular.
I would advise selling cheap cat adopts. And once you have enough money, try dragon and griffin adopts.
Step 4:The Price
One word: cheap. If you're just starting out as an adopt maker, chances are you're not very good. I know I sucked at the beginning, but I looked at other adopts an learned new styles, how to color better, etc.
Start off with selling them for 1-3 points, then you can increase them as you go on and get more popular. If you have a good adopt, but you're not sure how to price it, I'd advise name your price. I do this for my griffin adopts, and I can get a lot of points for them. Name your price is when people tell you what price they would like for the adopt. It's also called offer to adopt, an it's a pretty good idea if you want to make points quickly. Though, sometimes this can be intimidating since people might not know what to offer and are afraid that they might offend you if they offer too low, but get ripped off if they offer to high.
Step 5: Don't be a Jerk
There are a lot of adopt makers out there who are, well, real turds. They lie, they cheat, they steal, just to make a quick buck, er, point. I've seen some people steal points from others through adopts, not just by adopt theft, but by declining service to someone AFTER they've sent the points, meaning the person bought the adopt and the adopt maker didn't give them the adopt after they payed for it.
It's just, not right, please don't be on of those people.....
Anyways, this is the end of my "tutorial" I'm sorry if I offended any of you, also I'm sorry for any grammatical errors I may have made.