I was fielding the following squad

Turr + VI + AT (28)

2X RG + AT (48)

2X AP (24)

vs.

Nera + PTorps (30)

Horton + BombLO + ABT + SC (29)

Dash + Mang + Nien (41)

I quickly managed to get 1 tie on the Y Wing, on TI on the B-Wing, and 1 Tie and the RG on the YT. Despite my best efforts, I twice got within range 1 of the Y-Wing and my first AP succumbed to unavoidable ABT shots.

The B-Wing shot torps at Turr, which were easily avoidable with AT. But bad dice rolls against Dash's turret and the Y-Wing's (Turrs ABT hit was the first time I'd seen that card played) killed her off as well. My remaining forces managed to get Dash down to 1 HP, the B-Wing with no shields, and the Y-Wing to 1 SP before being destroyed, once again, I did 1:1 damage between my forces and my opponents with the Rebel shields being able to pick up the damage with no losses.

Should I be focusing all my ships onto 1 target and allowing the others free reign to shoot at me, or was this just a bad game on my part?

Ideally you want to kill a ship, as dead ships cant shoot. even a 1 hit point ship can shoot back at full effect (depending on crits of course).

All your ships at range 2 of something pump out 13 dice worth, which is enough to kill any of those ships (depending on dice rolls of course).

So yes, you need to focus fire, but also stay alive longer then your opponent. Thats the joy of x wing.

To me, it's not an "or" question, it's an "and" question. Your ships should split up, especially with interceptors, because it makes you harder to block, and makes you into a better blocker if you move first. But while you are split, you need to focus down ships and take them off of the board. That's how you keep your ships alive longer. So attack the same ship from different angles, say with your ships at range 2-3 of each other with overlapping firing arcs. Learn to fly like that and I think games will work out better for you.

Also, everything that nurglez said.