Reddit reviews Linguistic Fieldwork: A Practical Guide

https://www.amazon.com/Linguistic-Fieldwork-Practical-Claire-Bowern/dp/0230545386

If OP want's a guide, then Bowern's 2008 "Linguistic Fieldwork: A Practical Guide" would be a good place to start.

If you mean get into, as in you want to be interested but just can't find the motivation, what got me interested was reading about it. Learn from the best. Here are some good ones on documentation itself (I guess more on the eminence of languages dying and the need for documentation):

• Linguistic Fieldwork—Claire Bowern
  
  
• When Languages Die—David Harrison
  
  
• Vanishing Voices—Daniel Nettle & Suzanne Romaine
  
  
• Endangered Languages—Sarah G. Thomason
  
  Fieldwork is often closely associated with typology, so here are some books that explain some of what's possible in the world's languages:
  
  
• Describing Morphosyntax—Thomas Payne
  
  
• Ergativity—R.M.W. Dixon
  
  
• Changing Valency—R.M.W. Dixon & Alexandra Aikhenvald
  
  And then there are reference grammars, often the fruits of fieldwork. Here are some good ones I've gone through:
  
  
• A Grammar of Tariana—Alexandra Y. Aikhenvald
  
  
• A Grammar of Hup—Patience Epps
  
  
• Basically any other one in the Mouton Grammar Library, plus here are some free ones from Language Science Press.
  
  Then again, if you mean get into it meaning what language should you pick and what part of the world, that's a harder question to answer. I feel like languages just sort of happen to people: they know someone who happens to come from a community of minority language speakers, or they have a friend who says they ran into an understudied language while abroad, or you yourself happened to live in that part of the world for whatever reason. It's hard to go study a language out of the blue because you need an "in" somehow, which is hard to purposely get, I think.