What sort of business?

If you're thinking of starting up a sideline, you probably already know what you want to do. But if not, here are ways to find your sideline.

I recommend: Office rent is tough to swing from a business that operates only part-time, so odds are that you'll run your part-time business at home. Work at Home Dot Com is a good source of prescreened home-based business opportunities, as is BeTheBoss.com. Some employment sites, including Monster.com, offer links to business opportunities that include part-time and freelance self-employment.

Act Now!! Make 10K or More in Your First Month!!!

If you read your spam or pop-ups, you know that part-time and home-based business hopefuls are the natural prey of scammers pitching sexy sounding business opportunities, such as ponzi and pyramid schemes. If you're looking online for your opportunity, protect yourself.

I recommend: ScamBusters supplies a guide to identifying potential scams, and directories of scams in play. The Federal Trade Commission offers its own tips for avoiding scams.

It's never to early to study the tax implications

You'll find a host of tax implications to sidelining, all depending upon the sort of business you choose. Part-time businesses generally must follow the same tax rules as full-time businesses, and will add to your tax returns such all-important items as 1099 forms, Schedule C, estimated taxes and self-employment tax. If your part-time business will have employees, the tax implications triple. If you know about taxes going in, you can make choices about how to structure your company to take advantage of all the benefits -- such as the home office deduction or the self-employed tax deduction -- while avoiding pitfalls, such as underpayment of estimated taxes.

I recommend: Watch the Internal Revenue Service's free Virtual Small Business Tax Workshop DVD. Check out Nolo's deduction tips.

Don't lose your day job -- or your mind

When running a sideline with any amount of entrepreneurial zeal, it's easy to allow your business hours to mushroom, leading to stress, poor performance at your day job, a neglected family and a neglected self. Work hard at your business, but set reasonable boundaries and stick to 'em.

I recommend: Set aside family time or, if you have no family, "me" time, and don't check email, answer your business line, or check voicemail during that time. Organize your business hours so that you don't need to take business calls or answer business emails while at your day job--remember, under law, your employer can read your email if it's on a company computer. Check out Setting Healthy Work-Life Boundaries and take WebMd's Five Tips for Better Work-Life balance.

Part time or not, it's still a business

Part-time business owners may tend to treat their businesses rather casually -- after all, it's just a sideline. But it's still a business. During your allotted part-time hours, work as if you were a full-time entrepreneur, with all the same responsibilities. Those include not only customer service, but also proper business accounting, billing and invoicing, office management, mailing and more.

I recommend: Open accounts with steady suppliers of paper and other office needs such as Office Depot and Staples; doing regular business with suppliers can help you stay on top of things and also more easily account for purchases. Use an entry-level business accounting program, such as Quick Books, to keep your books, and use small business tax software, such as TurboTax Home and Business, to easily import accounting data from QuickBooks into your tax return and to properly complete the tricky employment-plus-sideline returns.

Adopt the professional image of a full-timer

Your part-time business may have to compete with full-time businesses for customers or clients, so avoid looking like a dilettante. Present the image of a full-time business and clients will regard you as a player, even after they find out you're moonlighting.

I recommend: Consider creating a mailing address separate from your home to create a more professional appearance; a post office box or mailbox rental can take care of that. Set up a dedicated business phone line with voice mail and a professional-sounding outgoing message. Set up a company domain name and Web site, ensuring that both have professional demeanors (info@mortardynamics.com makes a better impression than skippy7143@aol.com).