As a graduate student, submitting papers developed from your coursework at conferences and volunteering for book reviews are good ways to begin your scholarly career. Papers you submit to conferences can later be adapted for submission to journals. There is an ongoing debate about the value of quantitative measures of publication records. Some disciplines and departments emphasize the importance of impact factors, some use altmetrics, and others use different methods to evaluate scholarship.
You may want to think about the intended audience for your article, the type of article the journal tends to publish, and how long it may take to be published in that journal. Another consideration to make is whether to make your scholarship available to readers through Open Access.You can use Ulrichsweb or Cabell's Directories to compare your publication options.