The only way to become an expert is to make tons and tons of beats. You probably don't want to hear that but you are only an expert when you have found your sound and can execute properly and the only way to do that is to make tons and tons of beats. Obviously there are the bare basics like creating a four bar loop, eight bar loop, 16 bar etc. understanding 16th notes, quarter notes, half notes and what not.
There are some gurus out there that know a lot of technical shyt like the in's and outs of FL, Ableton, MPC, Reason, Maschine, etc plus have their own sound. Not only do these people make good music but they are like walking manuals for gear or the gear that they use/used. Then there are 'experts' who dont know shyt technical but can sit down on FL or an MPC etc and put together great fukking beats. It all really depends on what type of 'expert' you want to become. You can read the manuals that come with FL and Ableton and utilize practical application (i.e. read something or watch a tutorial then do it yourself) and become a technical expert while you make beats then make more and more beats and become that technical expert or you can say fukk it and learn what you need day by day step by step as you craft and learn to make beats and more and more beats you make you'll become better. At the end of the day no matter which route you take you gotta make more and more beats.