sorry for putting owo in the title but that's what you deserve for picking this beta guide instead of my BIG WEINER guide. anyways there's nothing inherently wrong with having a small weiner or playing less aggressively and if that's what you enjoy/want to do then go straight ahead. that's why i'm making this guide too!
here's the whole idea: you should farm excessively in lane by staying there with the sustain you get from corrupting/biscuits. of course if opportunity calls you may fight during laning faze. still, you should try not to take many risks as your main goal is to largely out cs the opponent. pushing them off of cs with well predicted q's is a good idea as well.
ALSO EXTRA TIP: a defensive support (janna, lulu) is not necessarily a good idea just because you're going a safer build. sivir still likes strong engage supports to help her in lane faze.
ALSO EXTRA EXTRA TIP: just in case you didn't know; once you get stormrazor you can space your w (ricochet) autos to get 3 crits on an entire wave. this is super useful!
also normie tips: if you haven't played sivir before q is your best option for poke/engage as it does a lot of damage/has a lot of range and procs your passive. when someone is within range for a lot of poke use q (and/or) auto then auto reset with your w.

AND FINALLY: if you want to try out a more offensive based build (or see threat matchups) check out my BIG WEINER sivir guide here:
https://www.mobafire.com/league-of-legends/build/9-1-easy-big-weiner-guide-to-sivir-huge-weiner-cool-537581