Alright, this is one of the variants of RUG Midrange, it's known as RUG Shackles. Above I have a decklist I built for this Variant, however, you should read the below choices and see if there are any changes you would make to the deck.
As the name implies it runs a card having to do with Shackles, that card is Vedalken Shackles! Because of the nature of this card, this deck is very fond of Islands, and the colour Blue. Much more so than any of the other RUG variants I included.
This is a very control themed Variant, I just thought I'd show you this first because the card choices are kind of universal among RUG variants.

The Core:
3 Snapcaster Mage
4 Tarmogoyf
3 Vedalken Shackles
4 Lightning Bolt

These choices should be pretty self explanatory, but since you've never played competitively, I can see why they wouldn't be. But rather than go over them in huge detail, they get a brief summary.
Snapcaster Mage: He lets you cast a spell again, when you opponent least expects it.
Tarmogoyf: Modern is full of Variety in card types, Tarmogoyf rewards you for this, and punishes your opponents for it.
Vedalken Shackles: This card helps deal with other creature decks very effectively. Also, it only matters if you controlled more Islands than the creatures power when you activate and resolve the ability. Meaning, if it changes later because of something, you don't lose control of it. (Something we'll cover more seriously later)

~Other choices~
Creatures
  Kitchen Finks. Kitchen Finks is an old fan favourite of mine, he's very good in the right setting, and sometimes even amazing. For one, he's a 3/2 for 3 that gains you 2 life upon entry. That right there should be enough of a selling point, but if it isn't, he also comes back if your opponent wastes a kill spell on him. In the right meta he is a powerhouse. However, since we don't run white in this deck, he costs GG to cast, which sometimes can be a pain to negotiate, especially when you're hoping to cast Cryptic Command in the same game.

  Young Pyromancer. Young Pyro is a decent choice, he helps with a swarm heavy meta mostly, by taking the heat off of you later in the game. If you run a lot of instants and sorcery's he can pay for himself in no time. However, he competes with the two drop spot normally reserved for Goyf, this can sometimes be an issue, but not always.

  Goblin Guide. GG is a one drop for a 2/2 with haste. That's almost always good, but sometimes it's not great, if your opponent knows you run plenty of him, they might be inclined to keep a hand with less land than normal. (Since you're helping to dig for it.)

  Monastery Swiftspear. Taylor Swiftspear is our other one drop of choice, again, she has haste! That's great! And the more spells you cast during your turn, the better she gets! Even better! The only issue is, she really only hits for 1 on the first turn most of the time.

  Scavenging Ooze. Scooge is a good card. He has it all! He's a two drop, that gets more aggressive, hits cards in graveyards, and gains you life sometimes when he hits things! Only one problem, he doesn't play nicely with Goyf, they're both two drops, and one eats the graveyard, while the other relies on it.

  Spellskite. Spellskite is a very vile card, honestly if it were up to me it would be banned. However, when in Rome they always say. This little guy right here can take spells your opponent thought they were casting at you, and change them to himself. However, an important thing to know about him, is you can't change the target of a spell or ability to him, if he isn't a legal target for that spell or ability.

  Batterskull. Not truly a creature, but it comes with one attached. This is kind of reserved for grindy matchups where your opponent has somehow gotten past your Goys more easily than originally thought. Another thing is he works well with Academy Ruins when he's destroyed.

~Sorcery~
  Serum Visions. Serum Visions is possibly the best Blue sorcery there is right now in Modern. It replaces itself, it lets you scry 2, and if you use Snapcaster to do it again later, it's still worth it by far. I know you said you were interested more in instants, but this is definitely worth running at least 2 of.

  Gitaxian Probe. A very good piece to any control deck, you can cast it your first turn to check and see if there's anything you really need to counter or not, and it replaces itself while you do it.

  Pyroclasm. This is our Sweeper, this card clears the board of a lot of things we don't like. However, it also, sadly, leaves us open if all of our creatures had toughness less than two. Be careful when deciding whether or not to run this, it's a good choice if you don't care very much about the creatures you run.

~Instants~
  Electrolyze. This is one of my favourite instants. It splits the damage anyway you need it to be split, maybe 1 to that pesky creature, 1 to its owners face? The choice is yours! And it cantrips while it's at it, so it isn't a wasted card! One major downside though is the price, I find that 3 mana is a lot of mana to spend of a simple spell like that, but it might be worth it to you.

  Cryptic Command. Father control. This spell is the best instant in Modern right now. It does everything. Ready to swing for game? Opponent trying to Bolt your game winning creature? Just cast this bad boy and you can simultaneously counter their spell while tapping all their creatures so you can swing unhindered.

  Remand. This spell is amazing at buying time, but that's about it. It usually buys you one turn free of... whatever that thing was, and while it's at it, it gets you that card back so you don't lose tempo. However, it never gives a hard 'NO'

  Mana Leak. Not listed here, because I don't feel it fits this deck very well. Mana Leak is different from remand in that early game, it basically says 'no'. However, unlike Remand (Which almost always proves useful) Mana Leak can lose it's appeal late game when your opponent has plenty of mana to tell you to 'Go shove it'

  Spell Pierce. Also not listed here. This is Mana Leaks little brother. If your Meta is full of annoying things that people cast turn one, this guy is your new friend. Hitting everything except creatures, he's a good choice for a combo heavy Meta, but other than that, hr has the same flaws Mana Leak has.

  Spell Snare. Kind of an insult to injury kind of card. It hits a lot of pesky things that Modern likes, including (But not limited to) most other counterspells, Goyfs, Bobs, Spellskites and Snapcaster Mages. Those are all bad cards to go up against, especially when you're trying to run them yourself!

  Mutagenic Growth. Definitely more of an aggro card than anything else I've really listed thus far, this devious bastard is a 1 for 1 trade with your opponent most of the time. Another cool thing about it, is it can be cast while you're tapped out! Your opponent might block with something thinking it's safe, only to find out you had one of these in your hand! It also has an amazing synergy with Monastery Swiftspear!

~Lands~
The land choices are hard to explain, really you kind of have to take my word for it when I say these are good choices. If you want to learn more about land choices I can talk to you about that specifically, but really it's a hard subject to cover.

  So! Those are most of the choices that these decks have that are worth making! There are other cards that I may bring up in the notes on other decks. But these are the cards I would suggest using for this style of deck.
  The other decks don't have these little snippits on them, they just have the cores, and other cards they may run that this deck doesn't.