The GOP has just bought themselves two years to prove themselves to voters. In 2016 the next election cycle hits and they have to convince voters of three things (1) they deserve to keep Congress (2) they deserve to keep the senate and (3) they deserve to win the presidency. Some of those orders are taller than others. Keeping Congress should be easy, barring major unforeseen events. But the other two are another story.
Setting the presidency aside for a future discussion, let's focus on the second goal. Winning the Senate means that legislation will actually get past Harry Reid and reach the president's desk. Many of the items put forward by the GOP will get vetoed but not all of them.
As unpalatable as it sounds the GOP need to strike a note of conciliation. That is not to say that they should give up their principles. What it means is that they should make every effort to visibly try to reach compromises. That said, the compromises should not go beyond their BATNA (Best Alternative To a Negotiated Agreement).
For example, on Immigration Reform the president has said (today) that legislation making it to his desk will negate the need for executive action. That means that within a limited window, the GOP can work towards a bi-partisan bill. Taking their time reduces the president's leverage every day and therefore increases the GOP's potential outcomes. On the other hand, delay in any action risks the GOP looking like a do-nothing Congress.
The real opportunity for the GOP lies in two areas. Firstly they need to do something that strongly benefits the middle class. They can do this via making a more business-friendly climate in America or by any other means. But that is where the gold is to be mined. After 15 years of middle class stagnation, positive movement in that area will do wonders for the GOP - provided they make equal effort to ensure they are given credit for it.
There's silver to be mined as well and that lies in foreign policy. While recognizing that foreign policy is more under the umbrella of the president, the GOP have the leverage of treaty ratification, and legal levers to move America once again in the direction of leadership. Again this is a fine line to be walked. President Obama does not deserve to take credit where it is not due, and the GOP risk providing that for him.
The other danger is in trying to do too much. Not in the sense that they can overreach (which is a possibility but not a likelihood) but rather that they spread their efforts too thinly and make modest gains in many areas rather than big steps in a few key areas. Those big steps will make a stronger impression than multiple little steps and that could spell a very successful 2016. It goes without saying that a successful 2016 for the GOP will provide a much larger impact than can be made over the next two years.