Well that is a tough general question. It is often the case when you have a better position but not an actual material advantage and not a clear way to gain it. This is perhaps an obvious answer but the answer is that you should try to keep improving your pieces, place them on active squares, and improve your position further by either gaining space, opening lines in your favor, perhaps by trading pieces but in your favor, maybe creating a weakness or two in your opponent's camp, cramping his pieces and making them worse etc.
All of this is easy to say but implementing it into practice is far from easy and it requires a lot of experience, and we do fail in doing so even with the required experience.
A good idea would be to try studying something about creating plans in the middlegame or something about positional chess etc.
Understanding positional advantages
Thank you very much for answering, I will do my best to apply those tips when I play.
You are welcome.
They are general tips however, and converting a slightly better position into something concrete is extremely difficult to the point that it might be considered artistic in some cases. 
Hello,
Many times I get a positional advantage out of the opening (+1 or so) but I trade pieces or something, and end up with with an equal position.
What should I be doing to keep the advantage?
Thank you
The short answer is work out what side of the board the opponent is weakest on and you are strongest on. If its the king who is weak, prepare for an attack on that side of the board. However, if they're not weak there, then look for other places where they are weak - usually weak squares, pieces or pawn structures. Then use the better placement of your pieces to win that material hope this helps
Unfortunately, important squares are impossible to identify without context and are opening-dependent, but are usually in the middle.
Just watch lots of videos on the middle game, I suppose, is a place to start.
Thank you, do you think a chess book like a Jacob Aagaard's positional play or strategic play would be good?
Do a thorough research about specific books, because some books are too tough for specific rating. Perhaps this might be of some use to you for reference:
https://www.patreon.com/posts/27108166
Thank you, do you think a chess book like a Jacob Aagaard's positional play or strategic play would be good?
Aagaard's books may be too difficult - they are for 2000+ players
Easier books would be
"How to reassess your chess" by Jeremy Silman
"Chess Strategy for Club players" by Herman Groten.
or my favourite book: "Chess Structures" by Mauricio Rios. He is focussing on the typical plans based on the pawn structure.
Thank you, do you think a chess book like a Jacob Aagaard's positional play or strategic play would be good?
Aagaard's books may be too difficult - they are for 2000+ players
Easier books would be
"How to reassess your chess" by Jeremy Silman
"Chess Strategy for Club players" by Herman Groten.
or my favourite book: "Chess Structures" by Mauricio Rios. He is focussing on the typical plans based on the pawn structure.
I'll check out those books, thank you.
Hello,
Many times I get a positional advantage out of the opening (+1 or so) but I trade pieces or something, and end up with with an equal position.
What should I be doing to keep the advantage?
Thank you