Could you suggest me some apps I could use for this purpose?
Tune your guitar using a camertone, not an electric tuner.
There are some apps with ear training exercises and games that you can download to your phone. I use one un spanish calle oído perfecto, I'm sure there must be an English equivalent. I practice on the bus! 😄
well I am already doing this, except the meeting with another musician stuff and it doesn't make much of a difference
Every morning try recornize 30 chords, invervals, progressions. Meet with another musician, and play call and answer exercises
Try to do some vocalize and record your self so you can improve your singing..
I may assume that active listening and singing may be the simpliest exercise; singing harmony with different pitches and intervals; hearing music in your head to have it mentally trained.