One of prophet Muhammed's compagnions asked him :

  "O Messenger of Allah (?), I frequently invoke Allah to elevate your rank. How much of my supplications should I devote to you?" 
He said, "You may devote as much as you wish." When I suggested a quarter, he said, "Do whatever you wish, but it will be better for you if you increase it." I suggested half, and he said, 
"Do whatever you wish, but it will be better for you if you increase."
 I suggested two- thirds, and he said, "Do whatever you wish but it will be better for you if you increase it." 
I said, "Shall I devote all my supplications invoking Allah to elevate your rank?" 
He said, "Then you will be freed from your worries and your sins will be forgiven."

[At- Tirmidhi].

Abu Muhammad Ka'b bin 'Ujrah (May Allah be pleased with him) reported:

The Prophet (?) came to us and we asked him, "O Messenger of Allah, we already know how to greet you (i.e., say As-salamu 'alaikum), 
but how should we supplicate for you?"

 He (?) said, "Say:
 'Allahumma salli 'ala Muhammadin, wa 'ala 'ali Muhammadin, kama sallaita 'ala 'ali Ibrahima, innaka Hamidum Majid. Allahumma barik 'ala Muhammadin, wa 'ala 'ali Muhammadin, kama barakta 'ala 'ali Ibrahima, innaka Hamidum Majid 

[O Allah, exalt the mention of Muhammad and the family of Muhammad as you exalted the family of Ibrahim. You are Praised and Glorious. O Allah, bless Muhammad and the family of Muhammad as You blessed the family of Ibrahim. You are Praised and Glorious."'

[Al-Bukhari and Muslim].