It's very easy for Advent to seem like the poor relation to Christmas musically and it can be tempting to start singing carols during these weeks to fit in all the favourites. However, sticking with songs which relate to the Advent texts and themes can really help engage with the radical message behind the Christian season as a contrast to the commercialised messages we hear everywhere else at this time. In year B there is a focus on the urgency of waiting for the coming of Christ and the transformation that will come with it, with a particular focus on prophetic voices we hear from the margins.
You can find a YouTube playlist here with many of the songs suggested below.
Gathering
The cry of "Prepare the way of the Lord" is a strong text for gathering and Prepare ye (YouTube) from Godspell would make a great introit for a choir or band or could be adapted into a call to worship. You could also pick up this text with either Prepare ye the way (CCLI) or Prepare the way (CCLI) which are more congregational. This week is the first appearance of John the Baptist and so it would be very appropriate to use On Jordan's bank, the Baptist's cry (CH 334 / MP 538). A more general advent hymn would be Hark the glad sound! the Saviour comes (CH 277 / MP 210), one of the traditional Scottish paraphrases. Sound the trumpet the Lord is near (CH 280) can give a sense of seasonal anticipation while using phrases and themes from this week's readings.
If you are using an Advent candle lighting song this year then Christmas is coming (CH 282 / CP 34) and Advent candles tell their story (STF 165) would both fit the pattern of readings with its themes of Promise, the Prophets, John the Baptist, and the Virgin Mary.
You could consider using songs related to the texts as a response to a prayer of confession, with the chorus of Comfort, comfort all my people (CCLI) and Come, O Lord, and set us free (WGRG) both possibilities for this, possibly just using the first verse of the latter to keep it simple.
Word
You might like to use a short Advent song before the reading of scripture. This is a good opportunity to give some musical continuity to the season, either by using the same song each week or by using songs in a similar style. The following songs all have a similar text, praying for Jesus to come, but use a mix of English, Latin and Aramaic: Maranatha (MV 19), Come, come Emmanuel (link), Veni, veni (WGRG), and Veni Immanuel (WGRG).
There are also some settings of plainchant which can work well here as continuity through the season, with the simplicity of the music allowing an opportunity for the power of the words to really sink in. The Advent Prose (NEH 501) is widely sung throughout Advent while O heavenly Word of God on high (NEH 2) would be another option which could also be sung to many Long Metre tunes, for example Gonfalon Royal, Morning Hymn, or Warrington.
For this week's psalm there are a few contemporary lyrics which can be sung to well known tunes such as Lord, you have lavished on your land (PFAS 85A) to Melita, When this land knew God's gracious love outpoured (Jubilate) to Sine Nomine, and Your favour rested on this land (link) to the Sussex Carol (which would also set the psalm in a seasonal context). There are lyrics available for a new version of this psalm by Wendell Kimbrough called We wait upon you Lord (CCLI) which will likely be more guitar led and with a chorus which fits well with Advent. There appears to be no sheet music or recordings available at the time of writing but this could be an option in future years.
For a responsorial setting Righteousness and peace (PFAS 85C) is quite straightforrward to pick up. There is also a wonderful two part setting of verses 10-11, Faithfulness will spring up (LTACR 108), by the Taiwanese composer I-to Loh who is one of the most influential Asian church musicians. This is sadly very difficult to get hold of either the sheet music or a recording for but I have made a sample recording here. You could either sing this in full or just use the first two lines as a response.
Response
Lo, in the wilderness a voice (NEH 170) and Wild and lone the prophet's voice (STF 189) both take the lone voice in the wilderness as their starting point, asking what that should mean for us. Also focused on John the Baptist is Through the prophets (New Scottish). There are a number of songs directly inspired by the Isaiah text. Comfort Oh Comfort (CCLI) and Comfort, comfort now my people (YouTube) are quite reflective settings while Comfort, comfort now my people (CH 274) needs to be sung with greater energy. The latter could be used as an opening or closing song if the congregation know it well or as a choral introit. When out of poverty is born (CH 291) could also be used either as a response to a sermon if the theme ties in or as a closing song. Make sure to feel this song in 2 rather than 4. Wait for you (CCLI) resonates with the tension in the Epistle about our restlessness and God's patience.
I often find Advent is a good time to use Taizé songs as prayer responses, singing twice at the beginning to allow people to learn it then once after each stanza of the prayers. You can also have the instrumental accompaniment continue under the spoken prayers. For this week I would suggest Prepare the way of the Lord (Hymnary) which can also be sung as a round. There is a longing in our hearts (CH 720) could also be tied into intercessions, with its focus on why we long for God to come - for justice, freedom, courage, comfort etc.
Sending
During Advent it's natural to go out looking forward to the transformation that will happen when Christ comes again and there are lots of excellent hymns on this theme including The voice of God goes out to all the world (CH 283) and 'Thy kingdom come!' - on bended knee (CH 473) which has the excellent line "gird up your loins, ye prophet souls, proclaim the day is near". The time has come (WGRG) also looks at our part in this with a new text to the well known tune Sussex Carol, sending us out to "protest, praise and dance". Similarly, Hear the call of the kingdom (MP 1282 / CCLI) speaks of our need to answer the call to bring hope to the world. Long ago, prophets knew (STF 178) starts with this week's theme of the prophets but looks forward to the end of the Advent journey. And finally, while I suggested starting with some songs with similar titles, Prepare the way (CCLI) would be a great song to finish on if you want to tie the service together with these words.