I've recently came back from a volunteering mission in Morocco. I needed to pack light so didn't bring my full camera gear and didn't bring my flash. Now not having a flash means that many of the indoor lighting conditions I had to shoot at high ISO which normally translates to more image noise. However, I'm going to share a technique I've learned from another camera forum in the past which goes over how to reduce noise in low lighting shooting at high ISO which I think you'll find useful.
So here's the trick in order to reduce the amount of noise. Have less dark areas in the photo. Do this by over-exposing you're photo by 2/3 to 1 stop. This will brighten the dark areas and hopefully over power the random firing of the sensor, decreasing the noise. But wait, the photos are now too bright. Now what you do is in your RAW editor bring back down to the correct exposure by 2/3 to 1 stop. And presto a photo with less noise than if you shot with correct exposure. Now run your normal noise reduction software on this adjusted photo.
A few things to keep in mind:
What your shutterspeeds are. Since you are over exposing your photo, the shutterspeeds are slower. Higher potential for camera shake or motion blur. This doesn't work well if you HAVE to shoot at your highest ISO in order to stop motion. I use this technique in this way. And I'll use an example to illustrate.
ex. scene shot at ISO 1600 1/100 +1 EV and brought back down in RAW editor will have less noise than same scene shot at ISO 800 1/100 EV 0
Other thing to keep in mind are blow highlights because of the +1 EV. So may not work for all scenes if you need the info from the highlights or brightest parts of the scene (ex. candlelights, lace pattern on wedding dress, etc.)
So try it out. You can try a side by side comparison or test at home to see the differences. I theory it should work for all cameras but it will depend on the noise performance at high ISOs for you given camera model. I hope this helps in reducing the noise in your photos and increasing your acceptance ratios.