My experience of pattern drafting is that it's easy to do on someone else but much harder to do on yourself, beginning with accurate measurement. I learned at evening class, about 30 years ago, where we paired up for measuring and basic block drafting, so I'd recommend using a buddy to help - someone who has some interest in sewing/crafting.
In terms of how to go about learning the skill, it depends on what kind of learner you are - are you the sort of person who can pick up skills direct from texts or are you, like me, more 'monkey see, monkey do'? If you can self-teach from books, there are many, of which tI have are Winifred Aldrich's 'Metric Pattern Cutting' and 'Metric Pattern Cutting for Menswear', and Natalie Bray's 'Dress Pattern Designing', 'More Dress Pattern Designing' and 'Dress Fitting'. The Bray ones date from 60 or 70 years ago but are still in print, which shows you how well-thought-of they are!
If you think you need someone to teach you and you don't have any personal contacts who might, see if any of the colleges in your area do textiles and fashion, in which case approach them about extra-curricular classes.