We would suggest your First Blaster Modification to be a spring upgrade.
A stock blaster shoots around 85-90fps.
A simple K26 Spring upgrade will take your Rival Blaster to around 135fps.
This will feel like a HUGE improvement to your accuracy and effective distance.
After a spring upgrade, maybe look at some cosmetic Mods to personalize your blaster.
What was your First Blaster Mod?
Comment Below!!
An easy mod to do if you have limited resources (or have to wait around for shipping!) is to lube and tighten up the seals on your blaster. Just working with what you have and squeezing more efficiency out of it.
My first mod was perhaps an unadvised one, but a project I took up nonetheless. After being dissatisfied with my stock Rhinofire's performance (An elite blaster typically reaches sub-70 FPS), I gutted and modified it with custom flywheels and motors to fire closer to 125 FPS. Was a very fun mod, even if the Rhinofire isn't a practical blaster to use!
My first mod was in fact a series of mods on my Kronos. A metal T-pull, k26, and a hand gaurd which I have since removed but may be coming back. And I would strongly suggest the spring first. The added range and power as well as the speed of the round makes it alot easier to hit what your aiming at.