Well, that's a big subject, especially if you include the whole written Constitution and the crafty laws, such as the PATRIOT Act, that have amended it already.
Perhaps the first step is for US citizens to decide what sort of country they want. For example, if it's OK for kids to be massacred in school, then you need no reforms. If it's OK for cops to kill unarmed citizens, then you need no reforms. If it's OK for your government to intercept your private communications, then you need no reforms.
The country seems to be going down the Florida sink hole at a rate of knots but if you're happy with that, carry on. All the rest of us need is for your troops and government to mind their own business then you will find that the rest of the world will do the same to ya'll.