There are some general translation principles which are relevant to all types of translation.
1) Meaning :
The translation should reflect accurately the meaning of the original text. Nothing should be arbitrarily added or removed, though occsionally part of the meaning can be transposed.
2) Form :
The ordering of words and ideas in the translation should match the original as closely as possible. This is particularly important in translating legal documents, guarantees, contracts, etc. But differnces in language structure often require changes in the form and order of words. When in doubt, underline in the original text the words on which the main stress falls.
3) Register :
Languages often differ greatly in their levels of formality in a given context, for exapmle, the business letter. To resolve these differences, the translator must distinguish between formal or fixed expressions and personal expressions, in which the writer or speaker sets the tone.
4) Source language influence :
One of the most frequent criticism of translation is that it does not sound natural. This is because the translator's thoughts and choice of words are too strongly moulded by the original text. A good way of shaking off the source language influence is to set the text aside and translate a few sentences aloud, from memory. This will suggest natural patterns of thought in the first language, which may not come to mind when the eye is fixed on the source language text.
5) Style and clarity :
The translator should not change the style of the original. But if the text is sloppily written, or full of tedious repetitions, the translator may, for the reader's sake, correct the defects.
6) Idiom :
Idiomatic expressions are notoriously untranslatable. These include similes, metaphors, proverbs and sayings, jargon, slang, and colloquialisms and ( in English ) phrasal verbs. If the expressions cannot be directly translated, try any of the following :
a. retain the original word, in inverted commas.
b. retain the original expression, with a literal explanation in brackets.
c. use a close equivalent.
d. use a non-idiomatic or plain prose translation.
The golden rule is : if the idiom does not work in the L1, do not force it into the translation.
N.B. ( The principles outlined above are adapted from Frederick Fuller: The Translator's Handbook.) with small changes.