US market sectors
Yes, it is a good idea to invest in companies when their sector is outperforming.
I showed you in this post that Finviz can give you some information concerning the “strength” of the sectors in the US market. However, there is another instrument that can give you even more detailed information. It is sectorspdr, and I will explain it to you in this video. You can find it at http://www.sectorspdr.com/sectorspdr/