The base will make the biggest impact on your TC over time and companies don’t want to give you much room to negotiate because of that. Try your hardest to get the most base because it will move the needle and is guaranteed money vs equity which is determined by the stock price. It also determines your annual bonus.
The next best item to negotiate is equity. Equity is a little more flexible because you can make the case that the base is lower than what you expected. Be sure to calculate enough equity you need (not appreciated) at grant that equals about what you would lose by taking a lower base. Additionally, don’t forget to factor in the unvested RSU at your current company that you will leave. To make the case for higher equity is to let the recruiter know you are committed to staying with the company because it takes 4 yrs to vest fully.
After all that is done, then you lastly try to negotiate sign-on bonus. The case for sign-on bonus is to let recruiter know that this amount you want is what you will leave behind at your current employer for the annual bonus by coming to their company. Companies will gladly give you more sign-on bonus to make you happy at negotiation time and seal the deal because it is only a one time payment they need to make to you and psychologically, it makes the candidate feel like they at least got something by negotiating.
Of course having competing offers will greatly help you negotiate the above.