If--and this is a big if--you are also receiving child support from your ex-spouse, your ex can be required to pay maintenance as well as child support through the Washington State Support Registry ("WSSR"). If you are not receiving child support, only maintenance, you cannot use this option.
If your ex-spouse fails to make timely payments, you can make a motion to reduce the arrears of maintenance to judgment and use that judgment as the basis for garnishing his wages or bank accounts. Unfortunately, this means that you either have to let a number of late payments accumulate, or you have to make multiple motions to reduce the arrears to judgment. If your ex-spouse makes payments that are late by a matter of days, there may be little you can do other than try to develop a cushion for when the checks are delayed (I realize that this is much easier said than done).
If your ex-spouse fails to make payment at all, and he has the ability to make payments, you can make a motion to have him held in contempt of court for non-payment. The consequences of a finding of contempt are unpleasant, and being brought into court for nonpayment may improve the timeliness of his payments.
Best of luck to you as you prepare to enter the workforce during these very challenging economic times.