Making the Beracha
- One shouldn’t make a Bracha while one’s hands are dirty rather one should wipe one hands. 
If One Mistakenly Ate Without a Beracha
- If one already swallowed his food but plans to continue eating, he should recite a bracha before doing so. He should not recite a beracha if he doesn't plan to continue eating.  In such a situation, if possible, one should say a bracha and eat a little more. 
- If someone ate food without reciting the bracha beforehand, but realized before swallowing, the proper procedure will depend on which type of food he put in his mouth. If it is a food that will become disgusting if spit out, he should put it to the side of his mouth and recite a bracha. If it will not be disgusting to spit it out, he should spit it out and recite a bracha before putting it back into his mouth. 
- If one drank a liquid but forgot to make a beracha before it, and remembered before swallowing it, he should swallow the liquid and not say a beracha rishona on what he already drank.  If one has more drinks one should spit out what one has in one's mouth and then make a bracha on the other drinks one has. One can, however, think the beracha in his mind while the liquid is still in his mouth.  Others advise spitting it out as long as it is not a pressing situation where one needs those liquids in one's mouth specifically. 
- Even if one omitted the bracha rishona, he should still recite a bracha achrona if he ate or drank a sufficient amount.
Preparing the food
- The food must be in front of the one making the Bracha, otherwise, the Bracha doesn’t have what to be effective upon and one would need to be a new Bracha.  If the food that’s brought afterwards is of the same kind as the one that the bracha was made upon or it has the same Bracha as the food that we made a Bracha on originally. 
- Regarding the order of brachot for foods of the same type and different types see the Order of Brachot page.
Text of the bracha
- For every Bracha it’s very important to say the words as they were established by the men of the Great Assembly. Words that are crucial to the Bracha and if one misses one of them, the Bracha doesn’t count: Baruch, either Hashem or Elokenu, Melech, and HaOlam.  If the Bracha has a conclusion of Baruch Atta Hashem… then the name of Hashem is also crucial. 
- S”A 183:10 writes that one must sit while saying Birkat HaMazon and some say one should it while saying Al HaMichya. So agree the achronim including Yalkut Yosef 183:7. See Mishna Brurah 183:35 who writes that this is according to all opinions. Kaf HaChaim 183:51 and Ben Ish Chai Chukat 4 write that it’s proper to say Boreh Nefashot seated. VeZot HaBracha (pg 8) writes that if there’s a need one may be lenient and say it standing.
- Kaf Hachaim 158:53 Shaar haTzion 181:32, VeZot HaBracha (pg 8)
- Berachot 51a compares one who eats without a bracha to one who ate garlic, causing him to give off an offensive odor. Should he eat more garlic and increase the odor? One who transgressed by eating without a bracha certainly should not transgress more! This is codified as the halacha in Rambam 4:2, Tur and Shulchan Aruch OC 167:8 and Shulchan Aruch 172:1, and Vezot Habracha pg. 88.
- Berachot 51a quotes the opinion of Ravina that even if you are finished eating you can recite a bracha. He brings a proof from the fact that a convert or baal keri (a dispute between Rashi and Tosfot there) can say a bracha on his tevila in the mikveh after the tevila. The gemara rejects his opinion and distinguishes between the two because the convert or baal keri could not have said the bracha before but the person who ate could have. The Rashba 50b s.v. vehatanya quotes the Raavad who holds like Raavad but he argues with the Raavad and cites the Geonim who also held unlike Ravina. Shaar Hatziyun 172:5 writes that this opinion of the Raavad is a daat yachid which we do not accept at all. Therefore, Shulchan Aruch OC 167:8 rules that if he is not going to continue eating he should not recite a bracha. Yalkut Yosef Berachot pg. 118 and Aruch Hashulchan 167:18 agree.
- Magen Avraham 167:21 writes that, if possible, one should say a bracha and eat a little more in order to satisfy the opinion of the Raavad quoted in the Rashba. Mishna Brurah 167:49, Aruch Hashulchan 167:18, and Yalkut Yosef Berachot pg. 118 agree. Rabbi Meir Mazuz (Ish Matzliach 167: footnote 7) says based on the Beit Yosef that this is not necessary. The Madenei Yom Tov 7:33:9 writes that the bracha he makes midway through the meal retroactively covers all of the meal from the beginning of the meal and corrects having eaten without a bracha. However, the Levush 167:8 explains that it is only covers the food from that point and on. Shaar Hatziyun 167:45 and Shaare Tesvhua 206:2 cite the Madenei Yom Tov. Therefore, Or Litzion 2:46:12 and Vezot Habracha pg. 88 say that in a situation where you are saying a bracha on what you are going to eat, you should have in mind to cover what you ate already.
- Berachot 50b quotes three beraitot regarding what do in a situation when one ate before reciting a bracha. These beraitot appear to contradict each other. One says to swallow, one says to spit out, and the third says to put the food to the side of one’s mouth. The gemara explains that one should swallow if it is a drink, you should spit the food out if it won’t be disgusting to eat it after that, and you should put it to the side if it will be disgusting to spit out. This is quoted as halacha in Rambam Berachot 8:12 and Shulchan Aruch OC 172:1-2, Vezot Habracha pg. 88, and Chazon Ovadia pg. 68. Mishna Brurah 172:7 explains that the reason that one must spit out foods that will not be disgusting is because the gemara teaches based on a pasuk in Tehillim 71:8 that when reciting a bracha one’s mouth must be void of any object or food, so that it is “filled” only with God's praise.
- Chazon Ovadia Berachot page 68, Shulchan Aruch 172:1. The Gemara Brachot 50b establishes that if a person took a drink without a bracha and remembered before he swallowed he should swallow and not say a bracha rishona afterwards unless he has more to drink. The Rosh Brachot 7:33 quotes Rabbenu Chananel who says that if one swallowed the liquid one shouldn't recite a bracha afterwards. However, he then cites the Raavad who says that even if one finished drinking he should recite a bracha. The reason is that unlike the case of Ravina where one finished eating when one's obligation of bracha was lost since one completed his eating, by the case of the drinks one remembered that he needed a bracha before he swallowed though he was just unable to recite the bracha. Therefore, after he swallows when he can recite the bracha he should. Rosh Brachot 7:33 agrees with the Raavad. According to Darkei Moshe 172:1, the Rambam Brachot 8:12 agrees with the Raavad but the Kesef Mishna and Gra 172:2 disagree with that interpretation of the Rambam. Chazon Ovadia Berachot pg. 69 supports the Kesef Mishna. (See Maamar Mordechai 172:2 who writes that the Rashba’s version of the Raavad contradicts the Raavad’s own note on Rambam Berachot 8:12. Shaar Hatziyun 172:5 points out that it is a different Raavad.) The Shulchan Aruch 172:2 holds like the Rabbenu Chananel and Rama like the Raavad. Vezot Habracha pg. 88 agrees. Although Rama 172:1 follows the Rosh, the Mishna Brurah 172:5, and Eliya Rabba 172:1 say one should not recite a bracha rishona if he is not going to drink more (see a list of other poskim who hold this way in the Shaar Hatziyun 672:5).
- Chazon Ovadia Berachot page 70-71, Ben Ish Chai Matot 14, Kaf Hachayim 172:1, Pri Megadim M.Z. 172:2, Ketzot Hashulchan 55:9. See Pri Megadim A.A. 172:1 who explains that according to Rabbenu Chananel nothing is gained by thinking the bracha since the liquids were disqualified from a bracha once they aren't fit for anyone else to drink.
- Magen Avraham 172:1 writes that if one isn't pressed to swallow those liquids because either one doesn't need those liquids or one has more, one should spit them out. The reason is that one should spit them out is because doing so avoids the dispute whether one should recite a bracha rishona after swallowing, where the Raavad holds one should and Rabbenu Chananel holds one shouldn't. Mishna Brurah 172:2 agrees. Biur Halacha 172:1 s.v. v'ayno points out that it is only that ideally one should be strict for the Raavad to spit out the water if he has more but one who is lenient to swallow what is in one's mouth has what to rely on. Kaf Hachaim 172:3 writes that one should be strict to spit out the liquids to be strict for the Raavad and also not to benefit from the world without a bracha.
- Magen Avraham 172:2, Mishna Brurah 171:3, Kaf Hachaim 172:2
- Shulchan Aruch OC 206:5
- Shulchan Aruch 206:5
- S”A 214:1, Mishna Brurah 214:4
- Mishna Brurah 214:5