I'm not an expert, and may be doing this incorrectly, but here goes.  

I use poser for animation.

One thing I learned is animate in small pieces...or you will want to kill yourself.

But how do you make sure each small piece lines up with the last one?

What I do, (may be a better way) is FIRST, MAKE A COPY TO WORK ON, then copy all the last frames in the key frame editor, to the first frame. You can usually do it as a block so it's not too hard.

Then, using the frame indicator, set the end frame to 1. You'll get a warning about losing frames, but that's okay that's what you want.

If all went well, you should see your last frame scene/pose/action, in frame 1 of 1 frames.

Now you can add all the frames you want, and you will start off where you ended for sure.

Hope it helps someone.