One of the biggest copywriting mistakes I've seen over and over again is writing about features rather than benefits.  But, you say, I want everyone to know all about my great product.  How do I get them to buy it if they don't know about its great features?   Sorry to burst a bubble, but the truth is they just don't care.

What they do care about proves a basic truth about human nature—we're basically selfish creatures.  We care about benefits instead of features.  "What's in it for me?" That's what's really important.  What that means is that you need to know exactly how your product or service will benefit your readers, and then be able to convey it to them in terms they'll understand.

Another common mistake is writing to everyone.  Your target market cannot be "everyone".  If it is, nobody will truly get the message.  And if nobody gets your message, nobody is going to buy either.  

Determining who your target market is before you start to write will at the least, focus your writing.   And go even further than determining a broad target market if you can.  Narrow your target market to a niche market instead.  Who are your most important potential clients?  Determine who your most important target is and write directly to them.

Pick one topic and stick to it.  

Prove your authority.  You can use case histories, testimonials, cite important studies or use your own published articles.  The point is that people buy from experts.  Make sure that's what you are.  

Whether it's print or online copywriting, make it easy for them to respond.  Send a self-addressed, postage-paid envelope or business reply card if your copywriting a direct response piece.  If it's online, use convenient order forms and make them accessible from every page.

And while we're on the subject of ordering, if you don't tell them why they need to order now, they most likely won't.  

Procrastination, it seems is a basic human tendency.  So, if you don't tell them to order now, they'll most likely put it off until tomorrow and tomorrow and yet another tomorrow, until finally they've simply forgotten.

Entice them to order with limited time or quantity specials.  Create a sense of urgency about it so they really will order today.      

There's an old copywriting formula to keep in mind while you're writing.  It applies to any type of copywriting that sells.  That old formula is AIDA

Attention. Grab attention with interesting headings, photos, subheadings, etc. Your first headline really makes or breaks your copy.  It's the first thing read and possibly the number one deciding factor for your reader staying or leaving.
Interest.  Create interest with your first sentence and your first few paragraphs.
Desire. Stimulate desire with benefits, testimonials and case studies.
Action. Ask for action now with special pricing, combinations, limited time or quantity offers.  Give them a really good reason to buy Now.

Repeat your main benefit, and ask for action again with a P.S.  Interestingly the P.S. is the second-most read line in print and online copy.  Some experts say one P.S. is best, while others use two or three.

So those are similarities for all copywriting that sells.  How is online copywriting different from print?

Various studies have shown that the internet is a culture of its own.  The internet was originally a place for sharing free information, and it remains that way today.  In keeping with its culture, freely share information you've gained and you'll get more visitors.  And that also means to eliminate the hard sell, and practice the soft sell instead.

Remember that internet visitors are usually impatient for information.  They generally prefer shorter pages than you'd usually write for such things as a direct response package.  
A general guideline is to use half as much as your printed text.   Keep sentences and paragraphs short.  Break long copy up into more than one page, or use modules instead.  

Don't overload your readers with irrelevant content or links.   People came to your site for a reason, and that reason was represented in their search term.  Your page needs to be completely relevant to the search term, or they'll simply leave.

The internet is graphics-oriented, so use pictures, diagrams, graphs, and anything else visual to help convey your message.  And, unlike print, the internet can be interactive, so if it applies, use it.  

But, you don't want to over-do graphics either because your web site needs to load quickly.  If it doesn't load in less than 10 seconds, your potential sale is most likely gone.  He or she is probably checking out your competition!

Possibly the biggest difference between copywriting for any type of print and online copywriting is in the research.  You can write any print copy without using particular phrases, but you can't do that online.  Your online copy needs to be written around keywords that are put into search engines by prospects.  

Remember that there are lots of copywriting tips you can find free of charge simply by searching with you favorite search engine.  And there are several very good copywriters who have free copywriting tips on their web sites.  Two that come to mind are Bob Bly and Allan Sharpe.

So those are a few tips for your copywriting.  And I'd like to leave you with one final tip.  Many would-be copywriters worry too much about their writing.  Fear of seeing their copywriting in public, or even on a letter can freeze you into inactivity.  I would encourage you to give it a try.  

If you're copywriting for your web site, remember to research keywords first.  And then start with an outline if you need it.  Start by just writing a few phrases.  The point is—just start.  Don't be afraid of mistakes.  That's what editing is for.