This text intent to help you solve only simple monoalphabetic or polyalphabetic ciphers by giving you the resources you might need .
In my opinion the first thing you should have is a good tool to help you calculate statistics in the ciphertext , therefore I recommend : Crank(linux,windows) and CAP(windows)
CAP is more sophisticated , but crank is good as well.
Then you need to have a dictionary with many different word lengths , so you can guess words easier ,the best I've found with a categorisation like that is : Wordox Lexikon
To know Letter frequencies in the language your ciphertext is written is very helpfull and is a must.
Note : if you have statistics for other languages please let me know
The following is a stats example for the english language,
Letter frequencies starting from the most frequent :
e ,t ,s ,d ,n ,r ,y
The most common digrams starting from the most frequent :
th ,he ,at ,st ,an ,in ,ea ,nd ,er ,en ,re ,nt ,to ,es ,on ,ed ,is ,ti
The most common Trigraphs starting from the most frequent :
the ,and ,tha ,hat ,ent ,ion ,for ,tio ,has ,edt ,tis ,ers ,res ,ter ,con
,ing ,men ,tho
The most common Doubles starting from the most frequent :
ll ,tt ,ss ,ee ,pp ,oo ,rr ,ff cc ,dd ,nn
The most common words starting from the most frequent :
the ,of ,are ,I ,and ,you ,a ,can ,to ,he ,her ,that ,in ,was ,is ,has
,it ,him ,his