I had this problem, too. I started using the labels as small dots as Cobra suggested until I got used to spotting aircraft then disabled them altogether. I find that it's best to look for movement rather than a specific shape. That being said, DCS itself could use some improvement in this matter, perhaps by making light reflect from aircraft or something. Yo-yo is probably right about higher resolution helping a lot, but higher resolution means a bigger impact on frame rate, so keep that in mind.
Edit: Also, be sure to keep your monitor screen clean... I've lost count of how many times I've been chasing a spec of dirt... :D