A successful MLM / Network Marketing Company typically has one key element:
A consumable product. Products like vitamins and nutritional supplements, beverages, cosmetics, etc. Anything that a consumer uses on a regular basis and will consume during a specific period, so they will continue to purchase from your company. Companies that incorporate Home Parties into their business plan tend to be very successful as well.
Avoid referring to the business as "MLM" or "Network Marketing", they tend to convey a sense of pyramid scheme to the average person. The more 'politically correct' term is usually Direct Sales.
There is a recent poll on Repspace.com on what consumers feel is the best product line for business and rep success, and nutritionals / nutriceuticals won hands down.
You can also go to a site like MLMRankings.com and look at the top 10 most successful companies and will see that most are either nutritional companies, or home party companies.
Good luck with your venture.