We can start practicing timing.
Every song has a succession of chords that basically repeat over and again. Some songs use different chords for each part of the song (verse, chorus, bridge), while others use the same chords throughout the song.
The first step in timing is to understand these chord changes. There are many ways to do so about the concrete time for these changes, but you should be able to recognize them by ear.
Every song is divided into measures, which are repetitive segments of time.
Listen to a song you like and try to mark off every chord change (every measure's beginning) with a foot tap.
This activity is really important, and this is precisely the point where you will change chord.
You will be helped by the tablature. Every chord change is indicated by the name of the chord above the exact point of the lyrics where the change takes place.
Once you have heard a couple of songs and you can identify the changes, you can start to play your first song on the guitar.
Don’t panic - just relax and try it.
Remember that we are experiencing timing, so we will start with two simplified chords that you can easily change from one to the other and you should strum when the chord change comes. For this purpose, you will play two of these simplified chords, C and G, and play while you listen to the song.