In my Opinion here are the most important skills for an SF (since im training one for the U21 NT :D)
1. Outside Defence and Inside Defence
2. Jump Shot and Jump Range (some people like an inside oriented SF, but that makes no sense, just make a PF then haha)
3. Inside Shot, Rebounding, Passing (now a lot of people say that Rebounding is VERY important. To me, maybe proficient or prominent is good enough)
4. Driving (more important of course if the IS is really good)
5. The rest of the skills?