German loves™ its case syncretism, so finding the right declension can be a bitch if you don't happen to be a native speaker or somewhere on that level. Here's a table of the articles and their respective adjective agreement to serve as a cheat sheet. Yum, tables :3

With no article

= strong adjective declension

		NOM			ACC			DAT			GEN
masc. sing.		Ø	-er		Ø	-en		Ø	-em		Ø	-en
fem. sing.		Ø	-e		Ø	-e		Ø	-er		Ø	-er
neut. sing.		Ø	-es		Ø	-es		Ø	-em		Ø	-en
plur.		Ø	-e		Ø	-e		Ø	-en		Ø	-er

(Hint: Look at the forms of the definite article below …)

With definite article

= weak adjective declension

		NOM			ACC			DAT			GEN
masc. sing. def.		der	-e		den	-en		dem	-en		des	-en
fem. sing. def.		die	-e		die	-e		der	-en		der	-en
neut. sing. def.		das	-e		das	-e		dem	-en		des	-en
plur. def.		die	-en		die	-en		den	-en		der	-en

With indefinite article

= mixed adjective declension

		NOM			ACC			DAT			GEN
masc. sing. indef.		ein	-er		einen	-en		einem	-en		eines	-en
fem. sing. indef.		eine	-e		eine	-e		einer	-en		einer	-en
neut. sing. indef.		ein	-es		ein	-es		einem	-en		eines	-en
plur. indef.		Ø	-e		Ø	-e		Ø	-en		Ø	-er
plur. indef. neg.		keine	-en		keine	-en		keinen	-en		keiner	-en

Notes

• Kein is the negative form of the indefinite article ein, used to negate noun phrases (from Middle High German dehein):
  
   Ich habe kein Auto 'I don't have a car'
   not: *Ich habe nicht ein Auto
   but: Ich habe nicht ein Auto 'I don't have one/a single car'.
  
   Ich habe keine Angst 'I'm not scared'
   not: *Ich habe nicht Angst
   not: *Ich habe nicht eine Angst (Angst 'fear' is uncountable in this context)
  
• Also consider this list of noun inflection classes, which helps you to determine if there's a suffix going on your noun or not (or optionally, what with historical dative -e) and if so, which one.