Dagger Slide is based on a very similar number game: 2048. This can be an excellent way to practice the game as the game is free to download on iOS, Android, and can be even played on your computer.
One of the most basic strategies to 2048 is setting a corner. Choose a corner that you feel comfortable with and make that your building corner for your biggest number. For Dagger Slide this means picking a corner and using that for your largest dagger. From this pick a side of the board to build on. For example I like the bottom right corner and side for building. Basically choose a side that touches your corner.
Once you have set your side, avoid swiping away from the side to move pieces. Following my example of right/bottom, when I move daggers I move right and down while occasionally moving to the left. I absolutely never swipe from the bottom to the top. Doing this can very easily force your large number piece out into the middle of the board where it is hard to build.
If the bottom row is missing a dagger, or has daggers that can be combined moving left or right, this leaves the possibility of a dagger appearing in your corner spot forcing your big dagger away. The later in the game you get the harder it is to put your dagger back in the corner. Always pay attention to what is going on in your bottom row before making a move that may move your corner piece.
Your building row is best built in an ascending order so you can simply stack all of them together in one big move where you chain combine daggers in a couple swipes to get a level 10 dagger. Don’t forget your level 10 dagger cannot be improved and it remains on the board creating an obstacle that has to be built around basically shrinking your board by one tile.
However, all this information is better represented in video as visuals are extremely important to discussing this game. This video was originally made before Daggers became a cross server event. However, the strategies discussed in this video are still accurate, but any mention of level 9 daggers should be mentally changed to level 10 with their addition. If you are curious about purchasing daggers (I do not recommend it as a way of boosting your score) read more about it The Numbers Behind Buying Daggers.