It seems that the majority of exp comes from minion kills; so I've decided to come up with a build that will ultimately shred minions and give you amazing wave clear and thus amazing exp for your team.
Sylvanas has probably the best kit for wave clear being able to explode minions and regain her stacks by applying more damage!
I've included a couple more builds but the main purpose of this guide is for the split pushing build and all tips and damage quantities will be directed at that build.

How a game with Sylvanas usually goes.
Farm until level 4 while using 'Withering Fire'(Q) to trade and a couple of autos. After level 4 depending on the map roam to an objective and wait for your team to engage then follow in not using your 'Haunting Wave' (E) as it's the first team fight and you can use it for an escape or chase tool later; focus the squishies then secure the object and back to farming and pushing until level 16. At level 16 go to the next object and wait for several enemy members to group up and fire your ult hopefully the team follows up with the major silence on multiple people. You can use your E to follow up if you wish but be careful. immediately after winning that team fight don't back push as hard as possible you might get a keep if minions are on your side. Back and regroup and look at any objectives your team can secure easily without throwing the game. 1 last push should end the game now you have your ult back up. This time wait for your team to engage and follow up again as you'll be the main target now after carrying the last team fight. END.

-Tips-
- Remember your that 'Haunting Wave' (E) can be used as an ESCAPE as well as ENGAGE so if you don't know how a team fight is going to end DON'T use your E.
- 'Haunting Wave' can also give you a great refresh on your stacks on 'Withering Fire'(Q) enabling more pushing power or being able to turn a fight.
- If you're approaching a tower and see 1 is out of cannon balls attack the other as 'Black Arrows' (Passive) stops the tower from being able to attack.
- If you position yourself correctly you can even attack tower and only take 1 cannon ball to the face, stand to 1 side of a gate and attack 1 at a time.
- Try to time your ult to hit multiple enemies instead of singling 1 person out.
- When 1v1ing an enemy try start the fight out of lane and walk towards their minions use 'Haunting Wave' (E) to get extra stack and then use 'Withering Fire' to turn the fight.