Silvanna

Core mentalities:

-Mage emblem + Bonus Magic damage (this also increases shield of 2nd skill) + Spell lifesteal = more survivability while still dealing good damage

-These emblems are there to balance being able to fight the opposing hero and clearing creep waves fast when needed during the laning stage. (Learn when to freeze lane or when to cut lane.)

Items:

-You can definitely change boots to Tough boots if needed. (Or Warrior boots but very rarely) 

-Only buy Divine Glaive if you truly need Magic Penetration in the exact moment or in the very near future. 

-Only buy Glowing Wand if you truly need an Anti-Heal item, otherwise just buy Blood Wings/Clock of Destiny or a Winter Crown instead. 

-Don't always autobuy Winter Crown. Check your team lineup if it's better for you to be targetable and tank damage so you can protect your squishy allies. 

-Every sustain type Fighter or builds should always have 1 armor item so you don't get destroyed by a single Sea Halberd. You should purchase the best armor item for the specific game. Even Dominance Ice is considerable which means you don't need to buy Glowing Wand in that scenario. An early Warrior boots + Dominance Ice as your first 2 items is considerable in some rare games. 

-Other anti-tank options: Wishing Lantern can work if they have 2 or more solid tank heroes. Cursed Helmet (-hybrid armor) can work if you can also utilize the tankiness that the item gives. 

-Battle Spell: Vengeance. It helps you survive and deal more damage. You can also look at your ultimate as a way of forcing the opponents into a "cage fight" which is a life-or-death situation and having Vengeance is very good there. 

••Feather of Heaven - Let's talk about this item. IT'S VERY OVERRATED. Sure, attack speed can make your 2nd skill deal more damage but just increasing your magic power in general also increases the skill's damage. Your ult also gives you a lot of attack speed already so adding more can be irrelevant. You can just get a different damage item that also gives some tankiness so you can actually do your job as an Exp laner. I'd say that this Feather of Heaven item is one of the main reasons why Silvanna doesn't feel that strong in general and why she's so low rated in Tier lists or Hero Ratings. Feather of Heaven can still be good sometimes if you really need to go hyper offensive due to your team lineup having too many tanky heroes but not enough damage output. That rarely happens though. The item is also considerable if you need do split pushing.