First determine what basic pieces you'll need, the kinds of bakeware that will cover the majority of your baking needs.
Basics can include the following:
• 8- or 9-inch round cake pan
• 8- or 9-inch square cake pan
• 9" x 13" cake pan
• 9" pie pan
• 9" x 5" loaf pan
• 12-cup muffin pan
• 11" x 17" cookie (baking) sheet
• 3-quart casserole dish
Cake pans, loaf pans and even cookie sheets will also be useful when baking certain breads, plus some of the above bakeware will cover pound cakes, main course meals and side dishes.
In addition to basic bakeware pieces you should also have some essential accessories on hand, such as mixing bowls, measuring spoons and cups, spatulas, wire cooling racks and parchment paper or a reusable silicone baking liner to place on baking sheets. Silicone liners are extremely versatile, don't require any greasing, allow for items to just slide off after baking and are very easy to clean.
To expand your bakeware assortment, many interesting items are available, such as bundt cake/tube pans, ramekins for custards and soufflés, tart/quiche and springform pans with removable bottoms for easy release and decorating, biscuit and popover pans, angel food cake pans and even pizza stones. If you think of it, it probably exists.
See also:
Tips For Cookie Baking and
Cookie Baking Tips