When I was first getting started in Minneapolis I took note of other local bands who were somewhat successful locally. I was not yet. I sent these bands emails to the extent of "Saw your show last night. Love your sound. If you ever need an opener hit me up." As you may expect I never got a reply. Not one. These bands weren't rockstars. On the contrary, they only were only getting around 50 people out to their local shows. I thought at the time, what's the big deal? Why won't they let me open a show or get back to me. I'm good!
I realized early on that I was going to need to make my own success. Once I started becoming increasingly more popular in the region every one of the bands that I initially hit up began to take notice. When I was out at shows they came up to me and started up a conversation. None of them ever remembered I sent them emails.
Eventually many of the bands and I became close friends. By the time I left Minneapolis and moved to LA I had played a show with virtually every band that I had sent an email to.
I get emails all the time from young bands asking to open for me. This is not how you approach this. Let me say this again. If you're reading this and you have asked me to open my show (I know you're out there) pay close attention. The reason I didn't get back to you or did get back to you with an open ended "maybe," is because you have to understand how this works.
Until bands get to the point where they can sell out a venue regardless of the other bands on the bill, there will always be the necessity for a "bill buffer." No one wants to put a show together including bands that cannot draw. Not promoters, venues or other bands.
Bands that contact me to open my shows may think I'm a rockstar in their region, but I'm not. I need bill buffers for every show I play. So, if you can't draw more than your 20 closest friends and family, then most likely I (and others) will not see you as a viable bill buffer.
You have to make your own success. Figure out a way to build a following without the help of other bands. Once you have something to show for yourself then you have something to bring to the table. Instead of sending an email of "Love your band, let me open sometime," you should get to know that band. Go to their shows. Become friends, while building your own fan base. Then when you both have substantial draws then you can put a show together.