You can use Nephalia Smuggler to temporarily exile your creatures when an opponent tries to kill one, but there are trickier things to do with it. Target Blade Splicer to get another 3/3 Golem token if you just need to build an army, or swap out your Fiend Hunter's target when a bigger threat comes along. Looking for a more subtle trick? Attack with a bunch of creatures including a Tandem Lookout. After your opponent blocks, use the Smuggler's ability on your Lookout. When it reenters the battlefield, pair it up with an unblocked creature.
Between Dismember, Fiend Hunter, Righteous Blow, and Gideon's Lawkeeper, you have plenty of options for keeping opposing creatures tied up and out of the way. But if you have a Phyrexian Metamorph in hand, hold off on getting rid of your opponent's best creature until you've had a chance to copy it. With so many other ways to deal with creatures, try saving your Oblivion Rings for artifacts, enchantments, or planeswalkers.
When sideboarding, consider whether your opponent wanted to start attacking you early or was content to slowly take control of the game. If your opponent was aggressive, sideboard in Cathedral Sanctifier and Inquisitor Exarch. The life gain will help you survive the initial onslaught while you set up your devastating combinations. Mana Leak and Negate are great sideboard options for matches where you're more worried about expensive spells and creatures, usually ones that cost four or more mana.
When you're ready to customize your deck, think about which plays worked the best for you and which you enjoyed the most. If you like attacking with fast hard-hitting creatures like Mirran Crusader, try the Innistrad set's Champion of the Parish. It gets bigger for every Human creature you play, which works well because almost all of the creatures in your deck are Human. Do you prefer Nephalia Smuggler's jaunty bag of tricks? Restoration Angel can temporarily exile something once, and after the shenanigans you'll still have a large, flying Angel.