Are you on Raspbian Jessie? Run *systemd-analyze blame* (without the *'s) in terminal. This will show you how long each service took to boot. The longest boot times are obviously the ones you want to focus on. My longest service was hciuart.service, which is bluetooth related. I did not need this so I commanded *sudo systemctl disable hciuart*. You can look up the other services that add lots of time too boot, and figure out if you need them. Save a copy of your image before doing stuff you're not 100% confident in, in case you mess up something.
A lot of people have success with SamplerBox, but it didn't help so much for me, YMMV: http://www.samplerbox.org/article/fastbootrpi
Also make sure you're using a fast SD Card. I'm using a PNY 85 mb/s card. With that card, the above that I mentioned, it takes 15 seconds to boot to the LXDE desktop, then 7 seconds to have TunerStudio loaded. With this setup, I haven't yet got a TunerStudio Project loaded, but I can't imagine that would add more than 5-10 seconds. So in total about 30 seconds from power on to showing gauges.