Because human language is often ambiguous, no machine translation system in the world can produce translations as accurate as a well trained, professional, human translator, however, there are a few simple things that you can do to help produce more consistent, intelligible and accurate translations when using an online or machine translation system:

Tell the people you correspond with that you use an online or machine translation system

Write Carefully and Be Succinct
Online and machine translation systems are best at translating commonly used language.
It is best to use short, simple and clearly worded declarative sentences (no longer than 10 to 20 words). They produce the best translations.
Avoid sentences with numerous clauses (multiple ideas/phrases). By all means, avoid run-on sentences. If a sentence contains multiple ideas or thoughts, break them into a single sentence per idea or thought
Avoid using clichés, slang terms, idiomatic and colloquial expressions as well as overly complex words.
If the text was written by someone else, determine if minor editing can help make it clearer, thereby producing a better translation.

Avoid Being Vague
Take into account the literal meaning of words and try to use the literal meaning whenever possible. It may have been a "great" movie but in most languages of the world "great" literally translates as "big" not wonderful.
Try to avoid words that may have more than a single meaning and translation, for example, use "airplane" instead of "plane", "wonderful" instead of "great", "weapons" instead of "arms", "movie" instead of "film", etc.
Words ending with the suffix "ing" can often be ambiguous, for example "playing", which can be a noun, an adjective or a gerund. Whenever possible, use an alternative.

Check Spelling
Make sure that the text to be translated does not contain spelling errors. Misspelled words will not be recognized and, therefore, not translated. For Portuguese text, this includes diacriticals or accented characters. For example, the Portuguese word você (with the diacritical over the "ê") would not be recognized by any machine translator if spelled as "voce" (without the correct diacritical). See typing diacriticals/accented characters for information about setting up your Windows system to use the US International keyboard driver. It will allow you to type all diacriticals or accented characters used in Portuguese as well as all other Western European languages..

Spell check your text before translating by using your word processor's English spell checker.

Check Grammar
Check the grammar. If the text is English, you can use the grammar checker of your English word processing program.

Avoid Using Special Characters or Symbols
Special characters or symbols such as ±, œ, ‰, etc., etc., can often cause confusion for any translation program. When possible, avoid using them.

Avoid Abbreviations and Acronyms
When possible, avoid using abbreviations and acronyms. For example, many Brazilians use the abbreviation "vc" instead of "você," "tb" instead of "também," etc., while many English speakers commonly use acronyms such as "ASAP" instead of "as soon as possible", "FYI" instead of "for your information", "TGIF" instead of "thank God it's Friday," etc.. While it is better not to use acronyms, if you absolutely must, maintain consistency throughout the text.

Avoid Punctuation Errors
While some punctuation may be a matter of personal preference, it is important that the punctuation of the text to be as standard as possible. The most important thing to ensure is that every sentence is ended with a period or question mark (a full stop). This is because translation programs usually verify the structure of a sentence before beginning translation.

There is some punctuation (e.g. parentheses, hyphens, dashes, colons, semi-colons, etc.) that, depending on the way they are used, can wreak havoc with any translation program. Wherever possible, avoid using them.

Do Not Omit Words
In certain English constructions, words such as "that, which, who", etc. are implied and, consequently, often omitted. For example, "I know that he went yesterday" often becomes "I know he went yesterday." Do not omit these words because they are normally required in Portuguese constructions.Additionally, in some English constructions, the article "the" is also often omitted (because it is implied), for example, "House and Senate". Always use the article "the" as in "the House and the Senate".