Why when the OP says “I can’t afford a teacher” are easily half of the suggestions “find a good teacher”? Anyway, working your way through Justinguitar.com online would be systematic and produce good results. Same with anyonecanplayguitar.co.uk. Both are a good mix of songs and applied theory. I also like yourguitarsage and guitarlessins365 for learning specific songs. All four of them are practical. The first two give the most theory. I think all are free.