Talk to a coach. Best if someone trained can watch you.
Most coaches will recommend using the inside edge of your sliding foot as a reference for where you are standing.
You can do an internet search on Personal Number to get more info on that.
Here is a start on it.
Note on Personal Number: It is based off of the Base Number for the bowler. Normal Base Number is usually between 6-8 boards. Base Number is how far the (center of) ball is from the inside edge of the sliding foot at release. In the example they use in that link above, they are assuming a Base Number of 7.
Knowing your Personal Number will allow you to know where to stand to play straight up the boards. To play different angles, you should talk to a coach, or maybe someone else here can help you with that. Not sure I can explain it properly.
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