I used (until I retired in 2012) be a nurse practitioner for bladder and bowel health. This was something I was knowledgeable in the past but did not want to give you out-dated information. However, it doesn't look as if things have changed very much:
The above is advertising a clinic but their list of suggestions is good; I like numbers 2, 4 and 9 particularly:
Timed voids. Urinate at least every three to four hours. Never hold the urine.
Double void. Before leaving the restroom, try to empty your bladder a second time. Focus on relaxing the muscles of the pelvic floor. You may try running your hands under warm water before your second void to trigger a relaxation response.
Drink plenty of fluids. Fluids keep the urinary tract hydrated and clean.
Have a bowel movement every day. The rectum is just behind the bladder. If it is a full, it can prevent the bladder from functioning properly. Increase your fruit, fiber, water and walking until you have soft bowel movements and don’t have to strain. You may add over the counter medications like Senna (Sennakot, SennaGen), Colace (docusate) or Dulcolax (bisacodyl).
Comfort and privacy are necessary to empty completely. Give yourself time to go.
Leaning forward (and rocking) may promote urination.
After you have finished passing urine, squeeze the pelvic floor to try to completely empty.
The sound of water can promote the bladder muscle to contract, but care should be taken not to promote bladder muscle instability with overuse of this technique.
Tapping over the bladder may assist in triggering a contraction in some people.
Stroking or tickling the lower back may stimulate urination and has been reported to be helpful in some patients.
Whistling provides a sustained outward breath with a gentle increase in pressure in the abdomen that may help with emptying your bladder.
General relaxation techniques can help people who are tense and anxious about their condition.
I used to do an ultrasound to see how much of a problem there was (and take urgent action if the person was in severe urinary retention). I also check that the person who I was helping wasn't taking any medication that would cause urinary retention.
I seem to remember cholinergic drugs like bethanechol helping and there's another that I can't remember but would not like to be quoted on this; ask your doctor or nurse prescriber. But you could use this as an example.
I was wondering about another symptom that you, or whoever this advice is for, may have.
If the speed of the flow of urine is slow when urine is passed and if there is hesitancy before the passage of urine commences and perhaps the stream is slow and weak in finishing, this should also be checked out by a medical professional. Also, if there is any dribbling urinary incontinence.