Let's say you used to manage a sports shop. Far better to make use of your experience and expertise by dealing in sports goods rather than something you know little about such as fork-lift trucks.
Other important considerations include:
Price
Is the product price competitive compared with other goods in your target market? Ideally your product should be slightly cheaper than the competition once you've accounted for freight, customs duties and other costs.
Demand
Does potential demand make trade worthwhile? Is demand year round or seasonal? How long might it remain in demand?
Competition
Are there any similar products available in your chosen market?
Safety and Legality
Is the product reliable? Is it covered under warranty? Can it be repaired if necessary? Are there any trade barriers preventing its export/import? Does it conform to national safety standards? Toys from the Far East, for example, are attractive to UK importers because of their low prices, but not all meet EU safety standards.
Suitability
Is the product suitable for your target market? For instance, electrical goods may be designed for the US's 110v supply rather than the UK's 240v system. Consider practical factors, such as the shelf life of food products, which may need to be long enough for shipping and storage. Additionally, bulky items can be costly to transport, making them potentially unsuitable for certain markets.
Above all, try to narrow down your choice of products early on. It makes the search for manufacturers and customers far easier, and it lessens the likelihood of having to drop a product after you've spent time, money and effort developing it and setting up contracts. Taking time to search for the right product is vital.
If it is particularly cheap and/or innovative you can develop a successful small business in a very short time.