Let's cut right to the chase, to keep you guys from needlessly toiling through fields of text:
I always get stuck at the world-building part, be it urban fantasy, swords & horses fantasy or sci-fi. It's the thing about writing that I do best, the individual story lines, not so much. My question is, how can I resolve this issue? And now, for the fields of text.
Once, I had written about 100 pages, but 75% of that was background and appendix type of material, just 25% actual characters and story development, something that normally is the meat of a book. Then, I normally get stuck on that part and get frustrated, ending with me not writing for a while, losing the feel for the story and tossing it all away.
In my opinion there are two possible solutions to this problem. The first being that I negate the problem completely and find a co-writer who is tasked with the majority of the non-world-building, while I do the world-building. The upsides of this are that it is most likely easier for me, and that you write more when there are two of you, as general rule of thumb. The downsides are that you have to find someone and, more importantly, that writing is a hobby, not my job. I study Medicine, and that will take priority. As a result, I might not have enough time to put into it to satisfy my co-writer, and thus drag their productivity down. That wouldn't sit well with me.
The second solution is that I work on my weakness. This would probably be harder to do, but would make me beholden only to myself. It would probably involve short stories.