Couple things that should help. First, it is generally a good idea that you clean the model with gentle soap bath and maybe a brush before doing anything, as there might be some residual silicone or other stuff from the casting process which can hamper the gluing.* Next, I usually scrape both surfaces that are supposed to be glued together. This will give the glue more area to work with. Also, I don't clean the surfaces from the dust that comes from scraping, as I think this facilitates the gluing as well. With even a bit bigger parts, I use green stuff as well as superglue. I apply the glue on both surfaces, then but a small piece of green stuff in between. has worked well for me. If you still have troubles, I would suggest you try another brand of superglue.
Hope this helps.
* Actually, just read from a post on another forum, that you should first bathe your metal miniatures in acetone, and then scrub then clean with rubbing alcohol. And they even recommended that you'd use ultrasonic bath instead of acetone, if you have access to one... Sounds like a bit too much to me.