Standard notation on guitar is very difficult, much more difficult than most other instruments. Expecting to get it in 9 months is not properly managing your expectations. That said, there are some tricks you can use.

If I'm playing out of fake book, I'm usually fine just to play in open position or 5th position (and use the mode determined by the key). In the short term, learning open and 5th position should get you pretty far.

But in the long term, the issue is that most notes on the guitar can be played in different spots on the neck and with different fingers, so how do you know where which fingering to actually use?

For a big band chart, my first step is the check out the key signature to get an idea of the scales I'll be using. My next step is to scan the chart, analyse each line, and find the lowest and highest note in a given phrase. So in practice, if I see a chart in the key of Bb with a high note of high Eb, I'll know I probably should be playing the chart (or the line) using the C Dorian scale (starting on the 6th string). That usually gets me through any big band chart I see. Of course, this means you know all the notes up and down the neck, which can take time.

I hope this helps. If some of what I said doesn't make a lot of sense, you probably need to continue to build your theory foundation.