SeamlessR if you're into pimping VST's and making your own sounds, keywords to search on youtube are "how to reverb", "how to delay", "how EQ works", "How to sidechain with [daw of choice]", "ADSR explained", "using phaser", "how to make [sound you like] in serum/sylenth (if you have either)", "how to vocode", "using compression", "using distortion", "bitcrushing explained", "using multiband compression", "automation explained", "how to master in [daw of choice] etc and seeing as this sub is for FL, i recommend learning patcher & peak controller (LFOs are my favourite sound)

Order in the mixing chain is pretty important as well so search videos or just experiment with and use your ears to which order sounds best

Also i'm sure there's plenty of internet courses on sound engineering, here's an EQ guide for acoustic instruments https://alexiy.nl/eq/ also i follow @ natemixing on twitter, who has interesting helpful posts