Once you sell RSU's the only option you are left with to reduce taxes is sell other investments, stocks/bonds/crypto, that are at a loss to offset the gains from the RSU sales.
But before you sell the RSUs you have several options:
1) Reduce your earned income by making/increasing pre-tax contributions to IRA, 401K and HSAs. So you reduce your other taxes
2) Use FSA, flex savings account, to pay for dependent care expenses and medical savings account
3) If your employer offers a deferred compensation plan for your RSUs, use it.
4) Sell it immediately on vesting, so no additional gains to be taxed
5) Make it a long term capital gain by holding it for a longer period.
6) Selling them over a period of time, to spread the gain out.
