For specific techniques on reverse image searching, see this post.
ImgOps is an extremely useful meta-tool for image operations. It incorporates the following reverse/similar search services: Google, Bing, TinEye, Reddit and Yandex, though all, except Google, perform poorly in my experience. The reverse/similar search services used to include Baidu Shitu as well, but has since been removed.
Baidu's specialty lies in identifying the name of the series from anime screenshots and manga pages, and sometimes even surpasses that of Google.[case 1][case 2] Its similar images feature is also often quite accurate. It may be a bit tough to use Baidu Shitu (Shi-tu, not Shit-u) if you don't understand Chinese. Nevertheless, Baidu is a serious contender to Google in the reverse image search department.
I also note some resources linked to by ImgOps that might come in handy at times: iqdb (anime), saucenao (anime+), trace.moe (anime) and ezgif.com. The first two are useful for finding anime wallpapers and artworks, while the last one can be used to break an animated GIF into its individual frames so you could cherry-pick the frames that will return a hit from reverse image search. trace.moe is a godsend gifted to us by soruly, which, at times, can even pinpoint the episode and time of an anime a screenshot is taken from.
Tip: If reverse image search didn't turn in anything useful at first, wait a couple of weeks/months and try again. The (full) image could have been indexed by the search engines during this period, so you might get lucky like me and find it in your subsequent trials.
Exercise: Crop the image from this question and reverse image search with Baidu. You should get something like this:
Although the romaji is given in this case (Chou Majin Eiyuuden Wataru), you should still know how to proceed from here if it weren't given. Copy the Chinese characters enclosed in either of the red boxes added by me, and do a Google search on those characters together with the word "English". It is not clear to me if one would be able to get the name of the other series (Madou King Granzort) without knowledge of Chinese: let's leave that as a challenge.