Don’t start with expectations of how good or bad you might be. Relaxation/mindfulness or task persistence doesn’t happen by magic, it’s a process and a skill to be learned like any other.
Start with achievable, small steps, e.g. if focusing on breath, limit it to five breaths that you mark up by moving a finger for each breath. Add five more as you feel more confident. You may want to start these at first your eyes open then try five or so with your eyes closed.

Be like a mother who is kind to a wandering mother. Be gentle but insist that you guide it in the direction you want to go. Simply notice what distracted you and go back to the details of your task. If you get cross, the toddler has won! Persevere and notice your achievements after every session.

The best way to help a wondering mind is to occupy it. One way is to be very, very interested in the details of what you are doing. In breathing, think what it feels like inside your body at the moment of each breath, what sensations are there. Focus on each breath as if it was the first breath you have ever taken. When doing a task, notice the details of what you are doing, the colour, smell, textures, movements required, etc. Focus on it as if you have to describe the experience to another person.