From ad-Dawal ila-Allah
Ramdaan is a time when all Muslims, all over the world, see much more of one another, whether in the masjids whilst attending the taraweeh prayers or in each other’s homes at the time of Iftaar. Invitations are eagerly accepted, which is a good thing, for among the rights of a Muslim upon the other is that when he is invited he responds  and that is in obedience with the Messenger's instruction:
“When any of you is invited to a dinner, he should accept the invitation…” 
Most of us are aware of the distinguished position a guest has in Islam, the right he has upon us of being entertained, as the Prophet mentioned in many Ahadeeth such as the following:
“He who gives food for a fasting person to break his fast, he will receive the same reward as him except that nothing will be reduced form the fasting person’s rewards.” 
What we’d like to draw your attention towards is how many times do we spare a thought for our host, the one who goes to the effort of preparing and providing food for his fellow Muslim? We can all relate to the joy and pleasure we feel when we break our fasts together, feeling in our hearts appreciation for the effort our host has gone to, feeling honoured that he/she took so much trouble for us. Yet many of us are unaware and unsure of how we, as guest, can 'express' our gratitude. Should we take a box of chocolate, or flowers, or perhaps make an impromptu speech after the meal to say how delicious the meal was?! Alhamdulillah! these are all good things, i.e. complementing and giving gifts to each other, but there is something we as guests can do which is highly recommended in the Sunnah of the Prophet (sallallahu alahi wa-sallam) and that is to supplicate for our hosts, after finishing the food, with any of the following.
1. Akala ta'aamaakul abraaru, wasallatalaykumul mallaa ikaatu, wa aftara 'indalkumus saa'imoon.
“May righteous eat along with you, the angels seek forgiveness ask Allah to send His Grace and Honor for you, and those who fast, break their fast along with you.” 
2. Allahumma at'im man at'amanee wasqi man saqaane.
“O Allah feed the one who fed me, and give the one who gave me drink.” 
3. Allahumma-maghfirlahum warhamhum wa baarik feemaa razaqtahum.
“O Allah forgive them, and have mercy upon them and place them in what you have provided them.” 
We should learn these supplications so that when we are invited to a meal and can express appreciation by supplication for our host with du'aas taught to us by our Prophet (sallallahu alahi wa-sallam) then never again should we feel stuck for word.
1. See Sahih Muslim (eng. Trans. Vol.3, p.1183, no.5379)
2. Narrated by ibn Umar in Saheeh Muslim (eng trans. Vol.2, p.727, no.3337)
3. Saheeh - related by Bukhari (eng. Trans. Vol.8, p.99-100, no 156 ans 160) frm Aboo Shuraih al-Kabee ans Aboo Hurayrah t.
4. Saheeh related by Ahmad [4/114-6 and 5/192], at-Tirmidhee [no.804]. Ibn Majah [no.1746] and ibn Hibban [no.895] (See Sifat Sawmin Nabee).
5. Reported by Ibn Abe Shaibah [3/100], Ahmad [3/118] an-Nisaa'ee in Ahmalul Yawm [no.268], Ibn as-Sunnee [no.129] and Abdur-Razzal [4/311] through various chains. Its isnaad is Saheeh. NOTE: The addition which some people give to this hadeeth: wa dhakara kumullahu fee man indahu [and may Allah make mention of you to those neat Him] then it has no basis here at all so be aware.
6. Saheeh related by Muslim (eng.trans. vol.8, p.1133, no. 5103) from Miqdaad.
7. Saheeh related by Muslim (eng.trans. vol. 3, p.1127), no.5070 from Abdullah ibn Busr (radhi allahu anhu)