How to improve tunnel vision?

I have difficulty in seeing the whole table, I focus only in some pieces. How I improve that? Sorry for my english!

I think that as you practice, you'll get better at this. It's always good to ask yourself a few questions before making a move. With practice you'll go through those questions faster and faster. Here are the ones I usually go through (they're not in any particular order):

1. Why do you think your opponent moved that piece?
2. What other pieces did this piece uncover? Are they a new threat?
3. What threats could this piece’s next move create?
4. Which of my pieces are unprotected?
5. Which of my pieces are being or will be targeted?
6. What does my opponent want me to do? Is it in my best interest?
7. What does my opponent want to do? How do I avoid that while also developing my own game?
8. What’s the situation and how do I veer towards a checkmate scenario? Which moves will help me achieve that?

I know they sound obvious but I think they're good basics for beginners

That is good advice, thank you!!

Practice scanning the entire board before making a move. Start from one corner and work your way across the entire board, checking the position of every piece.