There are many options for earning money in your spare time.  Here are some tips!

Consider establishing an offline business.  You don't need a brick and mortar location to start, and a local business has far fewer competitors than a website.  One example if being a personal caterer.  You could market to health-conscious professionals and offer a set menu at an affordable price for dinners or even pre-packed lunches.  This could be operated out of your own kitchen at a minimal investment.  You could also market yourself to local businesses with services like typing reports, copyediting, and so on.  If you come from a financial background in your career, you could also consider a side business as a financial consultant, which is another business which requires no inventory and a minimal capital investment.

For an online business, there are many options as well.  However, be wary of the many scams that are prevalent in the market before proceeding with any opportunity you discover.  Data entry work is one of the easiest and simplest work-at-home jobs and only requires a personal computer and some basic computer knowledge.  Freelance writing is also a good option for people who have a good command of the English language.  The ideal way of writing online is to find a repeat buyer who sends you assignments on a regular basis, typically via email.  Either of these can often turn into a full-time home business.  However, be wary of the many scams that are prevalent in the market. 

If you are a software developer, there are numerous businesses who cannot afford a full time software developer who may have freelance opportunities.  Small businesses and businesses often need to automate their systems or have other tasks that they would like to simplify with software. Visual Basic developers are most commonly involved in freelance activities and automation of small businesses. 

One other possible alternative is network marketing.  Network marketing businesses function by recruiting salespeople to sell a product or service, and then offer additional commissions based on the sales of persons recruited as well (called a "downline").  By increasing the number of salespeople you recruit, you can achieve income without actually making any  sales yourself.  However, be wary of multi-level marketing as it can be a poor choice if it requires a large up-front payment or has unrealistic sales goals.  Avoid anything that appears to be a get-rich-quick scheme, or that has unrealistic promises about the amount you can earn.

Also, a lot of network marketing involves you selling to your friends and neighbours; a quick way to lose them.