Keep in mind when you begin your TL that what time period you place it in will determine it's response.
If, for instance, you decide to do a TL in the 20th century, expect a lot of criticism. People in general are quite familiar with that period and if you suggest something outlandish (Japan winning the Pacific War with a POD after Dec 7th 1941 for example, or the Allies succeeding at Gallipoli, or the Me-262 coming into service in 1943 and turning the tide of the war etc) people will call you on it. Also the major events of the 20th century have been done quite often so there's probably a half dozen TL's in various stages of completion scattered across this site.
Not to say you shouldn't do one in the 20th century, if you don't mind the criticism, doing a TL like this can greatly expand the depth of your knowledge. Lord knows the criticism I received on this site on some of my earliest WWII TL's years ago definitely forced me to dig deeper and learn more. Not necessarily a bad thing.
Now if you don't want to deal with a lot of criticism, but want to gain a lot of interest and expand the breadth of your historical knowledge, try something outside of the well known areas of history. Though be wary of picking a POD that's too obscure or nobody will have any frame of reference to judge your TL by.