Consistenly Having Issues vs SI

I am struggling mightily against any half-decent SI player, and looking for some general advice on how to approach them.  I've tried to take various approaches against SI decks adjusting for previous ways SI players have beaten me, and it's gotten to a point where I'm losing a majority of SI games one way or the other.  

A major part of the problem for me is trying to "play around" Vengeance and Ruination primarily since I've gotten burned by either building powerful units to see them wiped away with a 7 mana fast spell.  Also, finding myself falling behind by holding onto big units, trying not to overextend myself in the mid/late game (knowing that they can drop a Ruination once I've gained control), as they are amassing & building up units through value plays like Ravenous Butcher or Chronicler of Ruin + The Undying/Cursed Keeper, Shark Chariot, and Barkbeast, etc.  

Most of my wins vs SI are with Noxus/Ionia hyper burn, applying as much pressure as I can early and hoping my early draws win me the match in the first 6-9 rounds which isn't fun or gratifying.  Sometimes I'll simply disregard the existence of Ruination, hoping the other player doesn't draw one and get away with it but I lose a lot of games this way too.  

Any input or suggestions would be greatly appreciated.  Thanks in advance.  

In terms of playing against Ruination, the best thing to do is to force your opponent to play Ruination by threatening lethal while still keeping some powerful units in hand. Since most SI decks will run a maximum of 1, maybe 2 Ruinations, once you've managed to bait out one you should be able to develop the board again and kill them without being punished. Open-attacking without playing a unit on your attack turn is also good if you suspect a ruination. You can also play a deck that wins through methods other than units, such as an Ezreal-Karma deck or Corina Control. You could also play shadow isles decks that run cards like Ledros that aren't punished by Ruination. 

The best tip against The Ruination is always remember it costs 9 mana.

When you have a decent board and you both have 9 mana+ in the bank, always consider to pass your turn without spending a single mana. 
So keep passing until he drops under 9 mana, as he can't pass forever or your units will eventually overwhelm him. 
When he does play The Ruination, you will have 9+ advantage to do plays or rebuild the board.

If you suspect your opponent is running The Ruination, follow these steps to play around it:

• Step 1: Build up a "sufficiently threatening" board
• Step 2: If they have 9 mana and your board is still threatening, always open attack
• Step 3: If they have 9 mana  and your board is  still threatening, pass
• Step 4: if they play something that leaves them at less than 9 mana, assess if your board is still threatening.  If it is, pass.

I can't really give you a guideline for "sufficently threatening", because its different for every game--e.g., against Corina Control you really don't want the game to go past Round 10, but for Warmother's Calling you arguably have more time.  The basic idea is the same for both though: YOU are putting them on a clock.  Even if you only have 6 attack on the board, if they have no blockers and only 12 health that means they only have 2 attacks to change the board state or they lose.  If they play a blocker, then you try to play just enough to match and restore the "sufficiently threatening" state.  For 9 mana Ruination takes close to if not entirely their options round, so you want them to play it either on your attack round AFTER you've attacked (they can't develop attackers) or on their attack round (they can't develop blockers).

The other thing to remember about SI is that is most of the current meta decks are pretty high-rolly.    For instance Cursed Keeper -> Butcher on Round 2 for 7 attack is just nuts--but that assumes you draw two specific cards practically in your starting hand, and both those cards can be very awkward without synergy.  Plenty of games where I've needed Ruination but instead keep drawing Vengeance, or vice versa.  In the big tournament this past weekend most competitors actually were doing control decks WITHOUT SI because they wanted some more consistency.  So when they do high-roll and draw the perfect answers just in time, accept that that's not statistically representative and move on.

I’m new to this games, can someone define a SI deck for me

Shadow Isles region.

Those are fun ones