Check to be sure your hematologist/oncologist is board certified in medical oncology if he is treating a cancer related problem and in hematology if it is a blood disorder.  Take note that not all specialists are board certified in both fields.

Your doctor should encourage a 2nd opinion if you have any concerns about the recommended treatment plan and should volunteer to assist you in arranging for such an opinion.

Make sure your doctor takes the time to explain his treatment recommendations and answers your questions to your satisfaction.  If he appears irritated by your questions or is unwilling to give satisfactory answers then it is unlikely that the patient-physician relationship will work to your advantage.