Trials that compare an intervention to two groups usually require randomization, where participants enrolled in the trial are randomly assigned to the intervention group or control group without prejudice. Randomization aims to ensure that one group does not end up with too many participants who share a characteristic with a greater frequency than participants in the other group. Table 1 in the study is where you can look to be sure characteristics are similar between groups. Randomization should be done by a computer or a predetermined plan, such as assigning people to a different group as they enter the trial (first person in group A, second in B, third in A, fourth in B, etc., though this process may not be appropriate for all trials).
