Soldering is the best way to go for the best possible connection.
That said, I have had good results using a small screwdriver pushed into the underside of the rail to pry it open slightly, then pushing the bare end of a wire into the gap. Remove the screwdriver and the rail will pinch the wire pretty well. Some folks Like to use a crimp connector stuffed in in the same way, but just the bare wire has worked fine for me. If you are unsure of your track plan or might be moving things around this works well. Of course you can also stuff the wire into the bottom of the rail then solder it as well for a solid connection that is invisibly hidden under the track.
While many of the newer track systems are much more realistic, I still think tubular is the easiest to use and most versatile of them all.
JGL
