I have assembled this White and Black deck, I haven't really played with it yet. But I was wondering if I could get some feedback on it.
Thanks!

https://deckbox.org/sets/711000

well, right now it's a bit random and all over the place.

here's some general advice that could help.

Consistency in magic is king - 1 of this and 1 of that, just doesn't make a cohesive deck that will work in anything but the most casual of settings where your opponent is as equally inconsistent.

You've got yourself started on a pretty aggressive curve and then you try to top out at 5-6 mana creatures and spells. You need to decide what kind of deck you want to build. Do you want an aggressive deck that comes out swinging or do you want to control the early game with removal and play big fat guys? either is equally valid.

My vote is to go low and fast. Get some more 1/2 drop creatures like Daring Skyjek and Boros Elite. Then back them up with some xathrid necromancers You want to top out at 3-4 cost cards and cut everything else. You'd also need a lot more creatures than just 21 you'd be looking at 26-30 creatures in an aggro deck that do various things

here's a few decks to look at for ideas.

http://www.mtgtop8.com/archetype?a=366&meta=52&f=ST

Your lands while 25 mana sources can support 5-6 cost, transguild pramenade is pretty awful at mana fixing. You'd be better served with more gates. Transguild sets you back almost 2 turns in mana production, it's just bad, cut it for more basics at the least.

I didn't have time to review your inventory, so I don't know what other cards you have. Elpablo's advice is good: avoid running a wide selection of one-of cards (one of this, one of that). Imagine what your ideal round would look like. What would you play on Turn 1? Turn 2? Turn 3? Build around those cards. Try to run four of each of those T1, T2, and T3 cards. From there, add some others to give you some flexibility, or to support the rest of your build. What would support it? It depends on what playing style you prefer. If you want to be aggressive, focus on creatures that give you an advantage on getting damage through: flying, unblockable, fear, intimidate, trample, etc. If you want to slow your opponent down for a few turns while you come on mid-game, play defenders and walls. It's up to you.

Come up with a statement about your deck that focuses on how it is going to win. For a Goblin deck of mine, the focus is to rapidly overwhelm my opponents by swinging on T1 and dealing loads of damage each and every turn until my opponent is dead (typically on T3 or T4). For a Merfolk deck, the focus is to get damage through using unblockable creatures (e.g., Triton Shorestalker) and other evasion effects (things that make my creatures fly, or make an opponent's land an Island) while I put Merfolk lords on the board (each giving my Merfolk +1/+1). I have another black/blue deck that is designed to force my opponents to run out of cards (by "milling" them--making them discard cards from their libraries). Knowing how you want to win will help you add focus to your deck.