If you are up against a good player, it can be difficult to get away with many of the best strategies you will find “in the book”, as they will have also studied the same strategies as you, and know how to counter them; though you should learn as many book plays as you can. It helps if you know how to do a fake gambit, to get them to take up a defensive position, but you are really planning something else.
It is important from your very opening move, to develop a plan of attack and not play 100% defense. Your plan may have to change, based on your opponents moves, but always seek out the best possible combinations in the next couple of moves made, for example; “If I do this, he may do this, so I will take his pawn and open up his rook.”
You have probably heard that the Grand Masters can plan 15 moves ahead or more. This is how they became Grand Masters, and it really isn’t that difficult once you learn how. Just look at what moves your opponent is likely to make, and think “If this, then this”, as many moves ahead as you possibly can. Do this each time you have some time to look at the board. While it is your opponents turn, plan ahead instead of getting distracted or daydreaming.
If you study the actual history of warfare, you will find many of the best strategies involve control of the center of the battlefield. This is also true in chess. If you control the center, you will have a major advantage.
Another good strategy for chess is to position your pieces to castle as early as you can - but do not actually castle. If you castle too early, then you allow your opponent more time to come up with a plan of attack, since your King is pretty much stuck in the corner, and you will find yourself on the defensive.
If you can open up both King-side and Queen-side for castling, then you have the option to remove your King to the best “safety” position, when needed. You should try not to move the three pawns that make up your King side castle, unless you absolutely have to, or can gain a q playing chess, as every game is unique.
If you find yourself playing the same person time and time again, be sure to vary your strategies, so they do not catch on to how you are playing and develop a defense against your style.