Achieving the iconic rise in choux pastry for Paris Brest can be a bit tricky, but several crucial tips can help. First, make sure your water, milk, and butter mixture comes to a full boil before adding in the flour; this step is vital as it allows the flour to properly hydrate and creates steam, which is essential for rising. When you're mixing in the flour, it’s important to stir vigorously for a minute or two to help the paste dry out slightly and cook the starches. After adding the eggs, ensure you mix until the dough is smooth, shiny, and can hold its shape but is not overly runny—this balance is critical. Lastly, do not open the oven door while the pastries are baking, as this can cause a sudden drop in temperature, leading to inadequate rise. After baking, allow them to cool fully before filling, which maintains the structure of the pastry and keeps it light and airy.