When is it good to trim blueberries bushes and how??

Do not do any trimming before the plant has produced fruit, usually not until after the second year after being planted in the ground.

If the plant is mature, and is just getting too big for your liking, then once again wait until it has fruited for the season, then trim it back to whatever size you want the plant/bush to stay at.

The season after this trimming may not produce as much fruit as the last year before trimming, but it will adjust.

I used a regular pair of garden pruning snip scissors, straight small blades.

https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-plant-pruning.htm

i only prune off the dead branches after it's leafed out a bit in the spring.