Is it a blazer (a standalone sportcoat) or the top part of a black suit? I believe black is one of the most difficult colors to make work, and perhaps that is the reason it doesn't get much appreciation in this forum (that may be an understatement).
First, do not try and match it to a pair of black pants. That will not be anything that looks good, nor will it have lasting value in your wardrobe.
Second, forget trying to get a loud tie or crazy shirt to make it more appealing. See next point.
Finally, if it were me, and I had to keep the black blazer, I would pair it with a pair of gray slacks (medium gray, not too dark and not too light). Then, I would find a complementary shirt/tie combination. You can bring some color into the shirt/tie, but do not go crazy. Tall, gray socks with polished black leather shoes and a plain black belt.
Importantly, where are you going to wear this?
It's the jacket from a suit (didn't know blazers only referred to standalone jackets...the things you learn)
I have some gray slacks from BR with very, very thin blue cross hatching. I definitely wasn't going to try and match it with black pants (not that much of an idiot). I have plenty of ties and shirts...I guess I'll just try a bunch on until something looks good.
No idea where I'd wear it. Not anywhere formal (and nowhere during the day since its a black jacket). The jacket has just been hanging there since I hate the pants (double pleated and outside of that, I dunno....they just fit and feel funny). I have another black suit which like but rarely use. I think I dislike the idea of having a jacket that I can't wear...
And yeah, I'm pretty sure the pants are beyond tailoring.
Final note: this forum is fantastic.