I just looked at your black deck, and although I don't have any specific ideas, I would like to give a bit of general advice. First, you need to cut out a few cards and put some multiples of the ones that work best together. For example, Phylactery Lich is an awesome card, but if you read it you discover that you need artifacts. Since I see no artifacts in the deck, it's an expendable card, and can be cut to add one of the cards that fits what you're trying to do with the deck. Now, looking at the cards, it looks like you're trying for life gain and discard, so that would be your theme. Don't try and do 500 different things with a deck. Pick one or two and roll with it. Anything that doesn't fit with your theme needs to have a reason to be in the deck, and if that reason isn't commonplace, it belongs in the sideboard. For example, Murder doesn't fit the discard theme directly, but it can be used to get rid of your opponent's creatures and will feed Blood Artist, which DOES play into the theme. Also, although it may never come into play, you can use it on your own creatures. I can't think of anything in Standard that you would target it with, but something like Graveborn Muse can outlive it's usefulness, and it would be a great way to get rid of it. Now, I'm gonna delve into Legacy for a situational card (since I'm really not familiar with Standard) and say Circle of Protection: Red for an example. It's great...so long as you're playing against a red deck. That's the kind of spell that shouldn't be in a main deck (unless you're running red and need to protect yourself from your own cards), but would see play in a sideboard. And finally, you need to look at your mana curve. Since you're not running any kind of mana acceleration, anything with over a 5 mana casting cost is probably not going to see substantial play time, as it would require at LEAST 7 turns (assuming you draw enough lands that fast) to get into play.
All that said, don't break the bank to get cards...what I do is build the deck I would like to build, and go buy/trade for the cards I don't have afterward. So just because you don't have four copies of Sign in Blood doesn't mean you can't put them in your deck. I will typically build a deck on here, then fish out the cards I have, and add what I don't have to my wish list. From there, I'll print the list out when I go to one of the local game shops, and know what I need when I trade on here. I will also prioritize my want list - that is, "I need X cards for deck A, Y cards for deck B, and Z cards for deck C." If I'm a couple cards away from finishing deck A, I will try and get those cards first, and go in order of completion percentage, so that I can fully build deck A in as short a time frame as possible. Also, take cards that you don't play that are reasonably sought after and put them in a binder, and take it with you when you go to buy cards. You never know who might have a card you need that they'd trade for something you may not be wanting to use...just be sure you know what the cards are worth so you don't shoot yourself in the foot