The elements of a good catalog can be broken down into Content, Structure, and Branding.

Content contains the products that are included, but there's more than just that to consider. The purpose is to give the reader all the information they need to decide whether to make a purchase or not. Product photographs are usually an essential part of this decision-making process. The picture should not be poorly lit, low resolution, grainy, or not well composed. It should be clear which product is being featured. Otherwise, the customer may judge the product's quality by the picture's quality and choose to buy elsewhere.

Professional product photos are well worth the investment. They can be used repeatedly and across multiple platforms (print catalogs, website, social media, etc.). 

Similarly, detailed and accurate product descriptions are also important to highlight each product's key features and emphasize the selling points. Product descriptions should follow a consistent format and strike a balance between providing enough information to help the customer decide without going overboard and becoming tedious to read. Like good product photos, good product descriptions are worth doing right. They can also be used many times and in many different places.

The structure is vital for a successful catalog. In case the products are not easy to find, or if the crucial information is confusing, the reader may throw the catalog away and look elsewhere. 

You should organize the products logically, with the different sections clearly indicated. The layout of each page should follow a similar format. Still, certain products should be more prominently showcased. The ideal structure is flexible enough to suit the product's needs while still being consistent. Above all, consistency is crucial to a well-structured catalog. If the catalog is confusing for the reader that reflects poorly on a brand and a company.

Branding is another essential element to get right and can make or break, even if everything else is done correctly. If a brand that is known for a casual, beachy style suddenly releases a very clean, modern catalog, loyal customers might get confused. Same goes if a high-end jewellery brand suddenly sends out something with cartoony fonts and bright primary colours. New customers might think they have the wrong website if everything is totally different from what they saw in the printed piece when they log on. Branding on a website, printed material, and social media should be instantly recognizable to everyone. Maintaining consistent brand guidelines will also help in having a consistent structure. Using the same images, product descriptions, fonts, colours, etc. that a brand is known for will go a long way in making a good catalog.