The routes are somewhat easy if you know which decisions to get the different scenes (see Sorrow85's guide
here). What's difficult and complicated right now is knowing if you're making the
right decisions when trying to get there.
There are so many variations even along a simple path like the Des Party path and it can be hard to know if you're making the right choices. For example, on this path you can help Eva with her assignment and have sex with or not have sex with her an say you'd want something more, or you can send her the paper and let het her come to stay with Viv where you can again have or not have sex, and if you go down the latter route then you can invite her to the party as well as going with Des.
Right now, since the game is still in early development and there's no clear walkthrough (Zoey Raven's is detailed as they always are, but the number of variables makes your head spin), it's hard to know just how these choices will affect future endings for both Viv and the LIs, so really you just have to do what you can to get the sex scenes and hope for the best.
Speaking of which, I've gone through what I presume is pretty much every path available so far and made saves for each individual one, but still have scenes I'm unable to activate. Namely, the Katherine scene at the party and an alternate version of the Viv/Des/Rebeca threesome.