My top tips:

Wash or at least rinse the garments as soon after getting them sweaty as you can.

Wash them with actually dirty clothes if possible. The dirt particles will absorb smell and act as an abrasive on the stains. If your clothes are generally too clean for this, use an oxy powder additive which will achieve the same effect.

Also: consider going without deodorant and antiperspirant and just use some isopropyl alcohol or similar to kill the bacteria in your armpits as needed; this results in less smell and less junk in your sweat to clean out of your shirts.

Lastly: wearing a technical shirt when working out will mean less sweat actually adhering to the fabric, making cleaning easier.