Jiu-jitsu is a complicated sport with a lot of techniques, and although being technically good is the key to good jiu-jitsu, it's just as important to know what techniques to use against a specific opponent and also when to use them. You have to be tactically aware as well as technically proficient.
Being tactically aware is basically the same thing as having a game plan. A simple example is that if your opponent is very good on top, you want to put them on the bottom, and vice-versa, for the best chance of success. Then within each position you have to understand what are the best options for you to use. If you are fighting a much larger opponent then closed guard and triangles are probably not going to be the best idea, keeping distance and keeping the weight off you by using feet on hips or butterfly guard should work out better. Then on the opposite end, closed guard will be strong against a much smaller opponent who will struggle to put enough pressure on to open it. If your opponent is big and strong, use movement and speed... if your opponent is small and agile, use pressure and tight control.
Outside of that general aspect of tactics, you also have to consider each position you end up in. If you have a really good guard pass but your opponent is positioned in a way to easily defend it, you should try something different. If you try to force a technique to work in a bad position you will probably come off worse. Thinking tactically means you also have to bail out of things at times... you might be halfway through a sweep, but if completing it means you will end up in a triangle it's time to give it up and accept you may fail on the sweep.
Another part of the tactical aspect is trying to pick up on things your opponent does during a fight. If you've tried your favourite submission attack twice and they've defended the same way twice, you can pretty much guarantee they'll do the same thing again... so be ready for it and plan your follow up attack accordingly. Similarly, whatever attack your opponent used in a position before, they will probably try the same, or something like it again. People will tend to go for the same techniques again and again as jiu-jitsu becomes an instinctual thing when you are fighting hard... so try to take advantage of this.
Competition also has a further angle on the whole tactical thing. You might have an awesome open guard, but if you are winning on points, have 1 minute of a match left and have 3, 4 or more potential matches to win gold... why open your guard? At that point you just need to try closed guard attacks, give yourself the easy win. Or a more extreme situation, maybe you are winning on points but are under your opponent's mount... you might know plenty of techniques to escape, but in this situation it's more tactically sound to just defend. If you escape you give your opponent a chance to score more points and while escaping there is much more chance of being submitted.
So, try to think on two levels all the time; what you need to do technically and what you need to do tactically. When you're in the heat of the moment you will react naturally, but by considering these things throughout your training you will make good tactical decisions naturally.