The most important 'starting question' is whether we plan on growing shade plants or plants originating from open lakes. The light requirements for the former is quite different from that of the latter.
Many default kits (tanks + light + filter and/or other accessories) come with aquarium light that don't produce enough light to grow more demanding planted aquarium plants.
Read this detailed guide on choosing the right light in terms of strength and spectrum.
All plants need a set of elements to grow well. Many of these nutrients are available naturally in our tap water. Fish waste also provides some. However, many elements will be still missing if we don't add them.
Optimal fertilisation is one of the core pillars for great plant health. We can achieve this through aquarium plant substrate (for rooted plants) and through water column dosing. Consistency is the key.
Read this detailed guide on what nutrients plants need to grow and thrive.
Carbon dioxide levels in natural lakes are high (10-40+ppm) due to decomposition of organic material, that builds up CO2 gas, compared to equilibrium levels (2-3ppm) in a standard fish tank that has no CO2 injection.
Having optimal levels of CO2 in the tank is one of the biggest impact factors on plant health and quality of growth as 40% of plant dry mass is made out of carbon. This directly also affects algae presence/absence in a tank as algae presence has strong correlation to overall plant health.
Skipping CO2 injection still allows us to have nice planted tanks - if we pay special attention to choosing plants that can grow well in lower equilibrium levels of CO2.
Read this for more information on the science of CO2 .