Hold the power button until the keys flash and a pop up comes up and says hold to restart. Continue to hold and you will get a full reboot. This is the equivalent of a battery pull and will clear out allot and should solve some of those bugs.

 

You probably have some apps running in the background that are slowing things down. Close all apps and go Settings > Apps > Running and see what is running. Settings, Google Services, Maps, and HTC Sense Input should be running, anything else should not be. If anything else is running it may be slowing things down and you may want to uninstall it to get a better performance.

I have also found that using the stock keyboard (which works fine) prevents lag over other keyboards (Swiftkey X, Thumbs Keyboard, etc). Uninstall them.

Also, the stock weather/clock widget works fine, while other ones like Beautiful Widgets and Animated Weather Widget consumed resources and caused lag. Uninstall them.

You can download the app Quick System Info that will give you detailed information about what is consuming resources.

I have been using Dolphin Browser for awhile but a recent update seemed to cause lag so I replaced it with Boat Browser, which runs much better.

Also, Android Assistant has some useful tools like the Cache Cleaner and System Clean that can help you take the trash out.

Don't bother with task killers, they unnecessarily use system resources. Android usually does a good job starting and stopping apps on its own, and odds are anything you shut off Android will immediately turn back on if it thinks it needs it.

As recommended, it doesn't hurt to completely reboot every few days, as it clears things out, too.

I do all of these things and I get pretty much no lag at all on anything but the more intensive games. Doing these things also saves your battery. This is a nice phone and a good OS if you know how to run it.

 

^Perfectly put. Ive been doing all these things and my phone works great. There is a little lag, but nothing crazy.