Assuming that you do not recreationally use the drugs being tested for, be sure that you are aware of potential false positives from prescription or over-the-counter drugs:
https://www.goodrx.com/blog/these-15-medications-can-cause-a-false-positive-on-drug-tests/
https://www.drugs.com/article/false-positive-drug-tests.html
It may also be best to abstain from consuming poppy seeds.
Background check could include verification of objectively verifiable claims on your resume (e.g. dates of attendance at school(s) attended, GPA(s) at school(s) attended, dates of employment at past employers).