"Stages" theory
There's a school of thought that says Magic decks basically have 3
"stages" in play:
- Stage 1: You're starting out the game, and have very little ability
to actually do most of the things your deck does. Basically this is
the stage where you can do very little on the board other than lay
land.
- Stage 2: You're able to play most of your cards. You have options
and can interact with your opponent. If you're both jockeying for
incremental advantage back and forth, your decks have both hit stage
2.
- Stage 3: You're able to play your biggest, nastiest cards (or play
them and pay for counterspell mana to keep them on the board, for
instance). Reaching this stage means being able to set up a
back-breaking finish.
How is this different from just talking about early game / mid game /
late game? Because we don't both get to the same stage at the same
time. Fast aggro decks basically exploit this by getting to stage 2
ASAP, then beating on your while you're still in stage 1 (or in stage
2, but lagging behind on board position because they've had a few more
turns to spill their hand out onto the table).
For a ramp deck or a control deck in this matchup, whatever your
"stage 3" is likely to be less important than how quickly you can get
out of stage 1. Ramp decks in particular are vulnerable to aggro
because they tend to spend their early turns on mana acceleration,
which is effectively staying in stage 1 longer in order to see a
quicker stage 3.
General anti-aggro strategies in ramp decks
The general approach to take, as you've said, is to "tie up" the early
game. Ramp decks usually can't race dedicated aggro (though some other combo
decks can), so this calls for a more controlling posture.
General strategies are similar to the anti-aggro part of a control
deck: sweepers, counters, and removal, backed up by blockers and tempo
cards to bog down the board. The problem is customizing the plan to
match your deck, which likely has other non-control elements in it,
and may be restricted by colors or the need to routinely tap out on
your own turn to advance your own game.
Conventional wisdom goes something like this:
Sweepers are (probably) best. If you look at recent(-ish) ramp decks like Wolf Run and Valakut,
you'll see that they tend to run sweepers (Slagstorm in red; Day
of Judgment in white). These give you the ability to undo several
turns of build-up in one fell swoop. Blue/green don't really have the
same option, though, aside from the very limited Creeping
Corrosion (which might be a good sideboard card against artifact
decks). The main downside of this approach is that, since most sweepers are sorceries, it does leave you a bit weak to aggro-control decks.
Run value-added blockers that enhance your Plan A. The other thing they do is turn their ramp cards into creatures, which
lets you get a nice blocker along with your extra land. Viridian
Emissary and Solemn Simulacrum are the go-to choices here.
Unlike mana dorks, it doesn't actually set you back to lose these guys
in a combat trade. (Note the additional synergy with board wipes!) These go great with a Birthing Pod gameplan, too.
Both of these strategies allow you to still play a proactive game and tap out on your own turn, which is what most ramp decks want to do.
Alternative approaches for blue/green
In the absence of good sweepers and low-cost removal in your colors, I
think you ought to rely on the creature solution mentioned above, backed up by tempo cards.
Let's look at counters first. The main problem with counters is that any turn you spend holding open counter mana that you don't use is a pretty big loss of momentum; dedicated control decks work around this by playing almost all of their low-curve stuff at instant speed (so, e.g., if there's nothing good to Mana Leak on a given turn, they'll just spend their mana on a Forbidden Alchemy or Midnight Haunting). Counters do have added value in protecting your big stuff once it hits the field, though, which can help when facing removal-heavy decks. If your have good mana sinks in your deck, then run counters; if you don't, I think you're better off skipping them.
Tempo cards are easier to fit into a ramp deck because you usually play them on your opponent's turn, but, unlike counters, you already know whether you'll have a viable target during your own turn, when you're deciding whether to play your stalling cards or advance your own board position. Vapor Snag has already been mentioned. It's a strong card in the current environment because bounce removes stockpiled +1/+1 counters and exiles tokens. Frost
Breath is another great card -- played right, it basically turns off their two biggest attackers for two turns. When you're playing for tempo as the bigger deck, remember
that these cards are no better than treading water unless you keep
making your land drops; throwing in filtering cards like Ponder
can help you to do that.
If a particular deck or card is costing you most of your games, it's
also reasonable to sideboard against it. For example, in the current metagame, Naturalize
is very effective against Red Deck Wins (hits their Shrine), Tempered
Steel decks (hits nearly everything in their deck, including Tempered Steel and Shrine of Loyal Legions), and most weenie decks (hits Swords, Honor of
the Pure / Intangible Virtue).