I usually find an author I like and then read everything by them until their back catalogue is completely exhausted. I find discovering authors new to me very difficult. Since most book reviews sound to me like they've been paid for, I'm only persuaded by recommendations from friends and family, or else those that I see here actually - I trust you guys and SFFChrons has helped me to discover many new SFF authors.
As for films, there aren't so many reviews here (when I first joined there were more TV and Film addicts but the membership is more of bookworms now). Anyway, I will watch most films if they come to broadcast or streaming TV since it is only a few hours investment of time (a book takes much longer to digest). Very few films are bad enough that I didn't finish them, and some are so bad they are actually good! Going to the cinema is different. It's more expensive than a book and involves a journey. I need to be inspired by both a trailer and recommendations that it is worthwhile. Recently, I've not been very inspired by the cinema, which is a shame because a film is much better enjoyed on a big screen and shared by an audience.
As far as reading a book after seeing a film goes, that has never worked well for me. The book is always spoiled. If I decide that I want to read the book, I'll avoid the film or TV series until after. Watching a film after reading the book is less problematic. I realise that there will be some changes, and that things might be different to how I imagined them to be, and I seem to be able to deal with those better than I read in posts by others on SFFChrons. Unless the whole plot is altered or some character acts in a widely different way, then it doesn't bother me.