The Mishna and Gemara in Maseches Brachos discuss the different criteria used to determine the proper order for making brachos. The four basic categories to determining the proper order of brachos are:
1. Most specific bracha (Hamotzei – Mezonos- HaGafen…),
2. Shivas Haminim (Wheat-Barley-Olives…),
3. A whole item, and
4. Personal Preference.
While in most instances one must follow the guidelines to determine the proper order of brachos, there are instances where a person need not follow the proper order. One common instance where this occurs is Kiddush on Shabbos. Based on the guidelines determined in halacha, one generally should make a hamotzei on the bread prior to making Kiddush. However, on Shabbos since Kiddush is required before a seuda we make a bracha on the wine before the hamotzei on the bread. This according to some Rishonim is the reason why we cover the bread while making Kiddush.
Similarly, if one is at a meal in which all the food being served at the meal is set up buffet style, he may eat the appetizer before the main course even if typically based on the order of brachos one should eat the main course first. R’ Bodner, in his sefer on brachos, quotes a Ritvah in Hilchos Brachos that explains that since it is the way of the world to eat an appetizer before the main course, one need not follow the proper order of brachos and rather one may eat the meal in its proper order.