Any Sivir Tips for a Bronze 3?

Infinity edge? Lord domminiks? Guardian angel?

After two items, you want to build according to the game and what you will be doing. That's not a simple solution but it's the best answer...

Infinity edge and lord dominiks are usually what you should build and then guardian angel if you want to stay alive or its really late game and dying will be a guaranteed death or get rapid fire cannon or shiv if you want to do more damage

This isn't so much build tips for Sivir, as much as a general mechanic/playstyle tips.
-Be careful of spamming her W in laning phase. It can be good for situational harass and is great if you need to keep a wave from getting pushed too hard against you, but tends to make it harder for many bronze/silver players to reliably cs.
-The higher you climb, be prepared for the enemy support to know the cooldown on your spell shield, and to immediately engage on you if you use it at an inopportune time. -Focus on being able to farm well. One kill is roughly equal to 20 cs. You will probably need your support's help to get a kill. Aside from the first few levels under turret, you do not need their help to cs. So, even if you have a relatively unskilled support, if you know how to cs, you can still guarantee yourself that gold if you know how to cs well. (That one isn't even a Sivir tip, more of just an adc tip in general)

Best of luck, and happy climbing =)

1. you don't need to learn sivir right now, you need to learn the game
2. watch streams of pro players and watch replays, especially the korean ones, there are channels dedicated to this in particular
3. after you learned how to adc start always with W, it's an auto reset (which means that resets the cooldown of your autoattacks so you can cast one more auto by pressing it in between) and not only it helps you to win trades better but also it has more aoe damage, and this allows you to push the lv2, also you can poke the enemy with the bounces
4. improve your mechanics, become fast and precise in pressing buttons, learning how to orb walk and to use the shield efficently
5. watching replays of other roles than adc will expand your game knowledge and not tunnel vision you on a single aspect of the game

If you have more questions just ask.

-edit- Oh, for the build i suggest ad reds, armor yellows, 6 cdr blue and 3 cdr per level blue and attack speed quints for masteries, pick ALWAYS no matter what warlords

for the build go you can go situational items such as