Well that's a little cheap Xizer...
I assume you're having trouble in eras 1-2, and maybe era 3. In eras 4 and 5, the NR fleet is as good, if not better, ship-to-ship as the IR fleet and close to being on par with the EotH fleet.
With the NR, your best friend is starfighter deployment or "spam." But the NR also has some fantastic options when using your frigates and corvettes. A group, say three each, of CR90s and DP20s (Corellian Corvette and Gunship, respectively) can carve their way through almost ALL of the oppositions fighters, and the Gunships' concussion missiles and dual turbolasers will give you some punch against opposing corvettes. Use that to clear the way for your own fighters and bombers to sweep in.
With X-wings and E-wings getting torpedoes (although at much slower firing rates than dedicated bombers), and the A-wings getting concussion missiles, use them to supplement your bombers' assaults on capital ships once they've cleared out the opposing enemy fighters.
As others have stated you can use your Mon Cal cruisers to take damage. Now you might try to use their power-to-shields ability to move them out of the fight once their shields start to fail but they're really slow. Sometimes you WILL lose an MC80 or MC80B as the AI tends to focus fire on these capital ships. Even if a ship's shields go down and you lose a couple of hardpoints, keep it moving. It can still clear the fight and its shields can recharge. But really the AI's tunnel vision can allow your smaller escorts to deliver a lot of damage. Keep in mind that the Mon Cal cruisers are also vastly under-armed compared to the IR's Star Destroyer counterparts.
The NR also has several smaller ships that are great damage "sinks". The Nebulon B series frigates are fast and maneurable to wade into the fight, unload a volley, take a few return shots, and quickly maneuver away to recharge their shields with Power-to-shields. Use your assault frigates and dreadnaught cruisers to deal damage while the AI's trying to take down the Nebulons.
And remember, KEEP YOUR SHIPS MOVING. Watch to see which ship the AI focuses on and rotate them around.
But really as the NR, if you properly manage your fighters you can cut down the opposing fleet's strength by half or more by the time your frigates and capital ships get to the fight. A big reason why is the AI is too dumb to congregate its fighters to meet your fighters head on, or to properly use lancer frigates and other corvettes to screen their capital ships.
And a general piece of advice, there are multiple Z layers, such as one for most capital ships, and I think there are three for most frigates (that's why you can have a frigate right above a capital ship but not one capital ship above another, which is weird cause I swear these battles took place in space!). If you can decipher which ships exist on which layer, you can bring in some 2D tactics, and use one ship to shield another from damage. For instance, if you have three assault frigates in a line, and you see the middle one taking a lot of damage because all the AI's ships are focus firing on it, move one of the two other frigates into the path of fire. It CAN shield the damaged ship from a lot of damage.
Hope this helps make your battles more enjoyable and fun. The TR team has done a great job of balancing a lot of each side's ships. No side is undefeatable. You just have understand each side's strengths and capabilities.