How to begin writing is a simple, but expansive question.
Do we mean, how to get organized? How to find the time to write? What to do once we commit the time? Or, how to actually begin? To some extent it depends on what you wish to write.
How extensive is the project? Do you wish to write a short email, or "the great American novel?" Regardless of what you intend to write, here are some tips,

• Determine what you wish to communicate - select the subject matter.
  It helps if you have some idea(s) of what you wish to write.
  This may seem like a silly statement, but actually it is common for people to not be clear on exactly what to write, let alone how to write it.
  
• Formulate your main points.
  This can be as simple as getting an idea in your mind, or as complex as sitting down beforehand and composing an outline.
  The outline should cover the main points you wish to make, and when you wish to make them - the sequence or placement of the ideas in the composition.
  
• Clear your mind of distractions.
  If you have details to explain and there are potential consequences to how well you explain them (like say, a letter grade for your composition, or a love letter to someone special), eliminate competition for your attention.
  Very few people can write well if they are at the same moment trying to watch television, or carrying on a conversation with someone in the next room.
  Any writing, but especially good writing, demands your attention and concentration.
  
• Do it - write! There comes a point where you can prepare, or stare at the ceiling, only for so long.
  You have to actually do it.
  Even if you are not well prepared or mentally composed yet, or you haven't completed the tips above, just do it; you have to begin.
  "Just do it" was a very effective marketing slogan for a sports equipment manufacturer for many years.
  At some point you need to make something happen.
  
• Proofread or reread your work BEFORE you send it.
  This is one of the most critically important tips.
  Never, ever - even if you are in the greatest of hurries - send your writing without first proofreading it yourself, or checking it for errors or meaning.
  Remember your written words carry impressions of you as a person.
  It is very important that your work is exactly the way you intend it to be read.
  What you send could exist for a very long time as a record, either for good or bad and whether the words you chose were appropriate, or not.
  

This last tip is critical, but there is help! If you are in a hurry to send your writing, or are not sure of the phrasing, the grammar, the spelling or the punctuation, wouldn't it be wonderful to have an all-serving writing wizard handy to instantly correct everything for you and reconstruct your words in the most effective manner possible? Think of the confidence and comfort such a wizard would give you, as well as the time you could save.
Well, there are English writing tools available that fulfill the function of this wizard.
They do all of the above, including grammar checking, punctuation checking, spell checking and text enhancement, with one simple click of your computer mouse.
They are the proofreader extraordinaire that you need by your side.
If Shakespeare only had it so easy!