Learning how your opponent thinks.

My dad and I regularly play chess, and at first I beat him very easily. But soon he learned my tactical play style, and could predict my moves and win. How can I make myself less predictable and adapt to the style of my own opponents?

Become a Jedi, use the force

I guess the answer partly depends on what your general chess philosophy is. Some people prefer to cast away all thoughts about the opponent and just "play the board", that is playing the objectively best moves in a given position. That's mostly relevant for higher professional play. For casual and amateur chess your best bet is probably to look at what kind of mistakes you are doing and work at improving them. That way you can outplay your opponent in that field, so they no longer can use their ideas to their advantage against you. These mistakes can be anything from simple tactical blunders to cramping strategic mistakes. Take a look at some general principles and try to apply them to your best ability.

Thanks a lot. I often wonder if I should take more risks, because mostly my pieces are left threatening attacks however overall my position is loose. Any positional tips would be greatly appreciated.

You know, I kind of do that with my husband. In general, he doesn't like to trade pieces. So, I use that to my advantage by playing something where I'm offering an exchange. He doesn't go for it and winds up moving somewhere that is not good for him positionally. Perhaps the best way is to go ahead and do something he might not expect -- maybe study a bit about other strategies or openings and try something different? If its just a friendly game, you have nothing to lose but everything to gain by learning something

I have no room to talk really. I suck! But I keep trying to improve and I get stronger little by little

Good luck!

bestpony has got it spot on, addressing mistakes is an absolute must.

There are too many different conditions you need to keep in mind for your games for me to be able to present anything of value regarding tips on positional play, saving the most basic principles, which you probably already know of (And then again, even these most fundamental principles have their exceptions, which sometimes can demand a very high mastery of the strategical skill of the player in question).

So, instead of, probably futilely trying to give you hints, I'd just recommend looking around this website, other parts of the internet and other resources such as books, depending on how serious you are about your game. This Wikipedia article can give a simple introduction, so you can see if there's anything you'd be interested in studying more deeply. https://en.wikipedia.org/wiki/Chess_strategy

And regarding your question about risky lines, if your opponent has given you a chance for a feisty attack you should definitely consider some more risky lines in your head. It'd be a good idea to have a wide grasp of tactical tricks and mating patterns to speed up this process. If you do find something that works, killing off some pawns to upen up diagonals and files for your pieces will be a worthwhile investment!