first and foremost tip for a yoga beginner is to “Come to the yoga mat regularly” meaning, develop the habit of regular yoga practice.
Second, do not be demotivated if you cannot practice certain yoga postures during the initial days. Some may have flexible body naturally and some may not. So, if you belong to the second category, it doesn’t mean that you are not fit to practice yoga. If, anyone says or thinks so, it is a myth. Fact is, anyone can practice yoga and if ones body is rigid and cannot bend or flex, it will for sure improve with regular practice. So, have patience and practice regularly with what your body supports and without forcing yourself just because someone else is able to.
Third, God has given each one of us different body structure and anatomy. So, do not compare yourself with anyone else. i may be able to perform twisting and binding postures with less or no effort but may struggle to practice back bending postures. And, for someone else, back bending postures can be like cake walk but twisting postures can be challenging. So, stick to what your body supports and practice regularly to improve comparing yourself to yesterday.
And now, what asanas to practice as a beginner? My suggestion for a beginner is to start yoga practice under the guidance of a yoga teacher.
Begin with Suryanamaskara or Sun salutations and depending on your current fitness levels , start with 6 cycles and gradually increase to 12, 24, 30 cycles.
Surya namaskara having 12 dynamic postures helps flex your body well and completely. Most yoga schools begin their practice class with surya namaskara as it helps warm up the body well and that helps perform asana practice with ease and prevents risk of injury to larger extent.
once you master surya namaskara or comfortable with surya namaskara practice, begin with some basic forward bending (wide leg forward bend etc) and twisting postures (revolved triangle, revolved chair pose etc)
suggest to perform these under the guidance of a teacher until you are familiar with the postures and alignment which is very important for: a) to get the effect on the right part of the boy b) incorrect alignment can lead to undesired results.