Looking for some tips from Xerath mains, and Twitch mains
Ok, as the title says I'm looking for tips. I feel like I can use the champions, but I'm having a lot of trouble... I'm going to try to narrow it down a lot. I know it's not so simple to describe how to play a champion in a few words. I've tried looking up guides, but I just can't seem to get results.
Right now, I'm taking a hiatus from actually playing league (I feel like my constant string of frustrating losses have made me unfit to play ranked; I'll just keep failing if I continue to play unranked, keeping me from being able to properly recover my playing ability). I figured, in this time, since I'm playing like trash, I'd see if I could get some advice from people who don't play like trash. Maybe I'll learn something.

I've been practicing with Xerath recently and playing against bots is really easy for me. However, in game, I have so much trouble with actual players. Even when I land my q's, they just don't seem to want to die. I end up poking most of the game, and either not getting any kills, or getting ganked and killed. I'm a lot better at placing vision than I used to be, but I swear that the junglers wait until the second my ward times out to come in and cc me until I die. I know Xerath is not mobile, so it's a very bad idea to go in unless you know for certain that you can secure the kill (i.e. low health, jungler is elsewhere for certain, probably should have your ult up). How can I avoid this stalemate?
Also, on mana management and starting items.... what items do you usually start on Xerath? I really don't like the results I've been getting with Doran's Ring; I usually get more out of boots and pots. Half the time, I bully them out of lane before they burn my second potion. I can often times afford either a good chunk of my archangel's staff, or a needlessly large rod on my first back.... Most of the time I feel like my passive is better than the Doran's item, especially if I can get easy aa harass on my enemy laner.
Overall, I think my Xerath game is getting the brunt of me being burned out, so it's hard to say where I'm going wrong.

My biggest questions with Twitch are mainly revolving around his q. How do you use this thing? I've seen people use this in such a way that makes him not just annoying, but downright terrifying. I can't seem to do that. I mean, you have to time it right, which is part of the skill in it, but I could use some pointers.
Another question I have came up while I was playing a ranked game... I was doing OK, but not carrying as hard as I've seen people do with this champion. Someone asked me: "Doesn't Twitch usually build BotRK first?" Most builds I've seen for the current patch, for Twitch as well as pretty much everyone else, rushes infinity edge, unless you need something else for the situation (i.e. hexdrinker if you have a roaming mid to handle, or a support that deals lots of damage like Brand). I've just been doing the standard IE into either bloodthirster or BotRK. Then I'd decide between a couple items depending on everyone's build... last whisper for if a tank is getting obnoxious and building thornmail, phantom dancer for if I just want more attack speed and crit, yommu's if it's somewhere in the middle... you know, standard adc stuff. Is there anything I've been missing that's really broken on Twitch?