In addition to two Redstone Ports connected by a Redstone Conduit (or even redstone dust I suppose), you can also use two Rednet Ports connected with Rednet Cable (if the Minefactory Reloaded mod is installed obv). I recently learned they do the same thing.
Whichever method you use, you right click on one of the Ports, drag the Battery icon into one of the Gray colored slots (I always use the one connected to the white square at the top left) and click "Commit". Then do the same with the other Port, except you have 2 choices on this one - if you want the reactor to just turn on/off when it gets full or empty, then drag the icon for On/Off into the same colored slot you used previously, and click "Commit". I prefer another method, which uses the Control Rod Insertion icon - drag that over and click "Commit". This icon will make the reactor run at 100% full power when the buffer is empty and it will run at 0% when the buffer is full. But the difference is, when you have 50% buffer, this setting will make the reactor run at only 50% of full power, saving you fuel. You have power in storage, so why run full blast? When you have 80% of a full buffer, the reactor will run at only 20% of full power - it uses the inverse of the buffer capacity. I much prefer this method, but feel free to use either one. Whichever you choose, you will def conserve your fuel which is what you were asking about.
By the way, you cannot fit two Rednet Ports into a 3x3x3 Big Reactor. So this is why I always advise beginning with a 3x3x4 tall reactor instead. It's pretty much the same power output as the 3x3x3, but it allows you to use the Ports to automate turning the reactor off when you don't need the power.
Oh, also, I think someone tried to tell me you don't need two ports, you only need one? Does that make sense to anybody? Have I been doing it wrong all along? I haven't experimented with it. I've always used 2 Ports with 2 lengths of Rednet Cable to connect them.