One greatly superior thing about it, compared to Fux, is that it relates the basic species counterpoint exercises (that Fux teaches) to actual music. It is much like Fux's method, but just better. That's the one to get started with (and it will be a great resource to come back to over time, too!). Seconding u/HashPram on the recommendation for Salzer and Schacter's 'Counterpoint in Composition.' REally great counterpoint text. It will get easier with time, you just have to do a lot of it. Bar a teacher, the only solution is to be methodical when analysing what you've written and keep re-writing until you get something that passes all the 'rules'.

I agree though - it is difficult to spot your own mistakes, especially when doing basic stuff like writing a cantus firmus. Really what I'd suggest is picking a decent text and sticking with it until the end because chopping & changing won't get you anywhere. Scribd can be a useful source of documents you're struggling to get hold of, but (like torrenting) the tendency is to get 10,000 books, half-read some of them and then give up after 6 months. I found Gauldin's books on Renaissance and Baroque counterpoint a decent buy.

Of the two Peter Schubert books, the one on Baroque Counterpoint is rare as rocking-horse shit (I'd suggest a library for that one, although you can buy it for the low, low price of $300 on Amazon from one spiv or another), but the Modal Counterpoint one can be bought relatively cheaply. My struggle with counterpoint wasn't really the species exercises but how then to broaden the application of what I'd learned into areas that aren't strictly contrapuntal but which clearly have a contrapuntal basis, and on that front this book is a goldmine. Salzer and Schachter's 'Counterpoint in Composition' is well worth the money.

Peter shubert baroque counterpoint pdf