Got my first neca alien, and it has floppy knees, which means it won't stand out of the box.
So what I did, was for every joint that was stuck, I used a dap of oil on a Q tip and worked it into the joints, and for every loose joint I squeezed a little white glue on the outside of the pegs and worked it in, moving the joint around until the glue drys and the joint is tighter.
Since my alien came with an Hicks, I noted that the shoulder light was supposed to fit into a hole at the back, but the hole in the armor and the main body was half an inch apart, which required some creative cutting with a hole punch.
If your kit isn't broken out of the box, I think it's fine to get one and work on it a little. Just don't play around with it too much.