Practice; what others are saying about the nerfs are true, but you can make any champion work with enough practice.
I suggest watching high elo players to pick up tips; pick a favorite pro (ie. Faker, Bjergsen, etc.) and look up a VoD on youtube; alternatively you can go on a channel like best one trick ponies on youtube and find a good Taliyah player.
As far as builds, I generally check op.gg for what's the most popular/common build/runes/mastery set ups, which give you a good starting point for how to build the champion (In my experience, the Korean server has the "optimal" set-up, but keep in mind there are some variations on meta between regions, in addition to certain builds working better for certain skill levels, so I also check the NA server and judge for myself what I think would work for me). Basically the goal here is to avoid pitfalls and traps as far as builds, less about finding some perfect, cookie-cutter build (since a "perfect" build is situational).
She was one of my if not my favorite champion on release; ever since they changed her W to vector cast I actually can't play her (I've spent a lot of time trying to learn Viktor and Rumble with no success; if I ever dedicate myself to midlane again, Taliyah is one of the champions I'll put a lot more time into, but I just don't have the time or motivation to practice her right now; still salty about the change, lol). General tips from when I played her:
- if your opponent has a dash, try and predict when they'll use it and cast E. Pretty obvious, but done well in practice she can really mess people up. It works better now since Talon no longer has a blink, so that's one less champion that hard-counters her.
- Don't underestimate the movement speed she gets from worked earth and her passive; she can get around lane and the map incredibly quickly.
- in general, think of space in lane the same as you would any other resource; you have to manage your space carefully or else you'll quickly run out of area to cast a powerful Q.
- try to keep your worked earth circles as close/overlapping as possible (ie. cast Q as soon as you leave worked earth), this way you have more space to work with.
- use your wards and use your lane, especially the sides near brush, to get off more full-power Q casts. You can "cheat" forward a bit in lane at the start of the game so you can use space on your opponent's side of the lane while the minions are still coming to lane.