When I tie braids, especially when new, I don't lube the knot, it will then heat up that lubricant and help the knot to hold.

If it isn't a braid ready spool, you need to either tie a few feet of mono on, then tie the braid to it and fill the spool (position this knot on the edge of the spool), or wrap the bottom of the spool with tape. I like to use electrical tape, it seems to be less messy. Like mentioned earlier, if not, the whole thing will slip on the spool after a while acting like the drag isn't working. For braid to hold onto a surface, it has to dig into something, the tape is something it can cut into.

Also spool it on as tightly as you can possibly get it, it will help with keeping it from digging into the spool. Use a little lighter drag also, that helps.

If you direct tie leaders on, a double uni knot will cut through mono, but will work well on Fluorocarbon. I use an Albright or one of it's derivatives, or the Slim Beauty knot, they work well with all leaders.

If you run into problems, your best bet is to take it to a place where you have enough room, tie the line to a tree and walk it off of the spool, then max the drag on the reel, reel it in using the drag on the reel to pull you along, this will rewind the reel quite tightly.