@Nugzilla 1) genetics 2) nutrients 3) proper lighting are the main factors for getting denser buds. I’ll list how I do it down below.
First get a cultivar that naturally has denser buds. Feed appropriately. High nitrogen and phosphorus with the right micros (generally calcium and magnesium) will increase branching and give you more “fruiting sites” in veg. Maintain a decent amount of potassium. They don’t need much early on but it is still essential. Just enough to maintain healthy growth.
As you get into flower you really don’t need to increase potassium until about week 2 or 3 of flower. So top dress with a potassium or flower feed at the first sign of preflower with autos so that they’ll get the extra potassium when they need it. If growing organic that is, because top dressing takes roughly a week or two to work down to the roots. If using chemical salts just feed at week 2/3 of flower or as soon as you see some signs of potassium deficiency. At this stage the biggest culprit for fluffy flowers is not enough potassium.
Keep your lighting in range. Around 500ppfd for veg and around 700 for flower is generally optimal. Not enough light your plants will stretch and have longer stems which equates to less dense bud sites. Too much light will stunt them too and decrease your yield. Make sure you do some light lst and just enough defoliation to allow for maximum light penetration. The second biggest cause for light fluffy buds is light stress or not enough light.
The last most common cause for fluffy buds or stretched out plants is heat stress. So try to keep your temps in range and make sure that if it’s too hot feed some silica and extra potassium and use some liquid kelp. Potassium is essential for stress recovery and your plants will need more if it is too hot. Silica helps stress recovery too and increases water retention in soil and circulation in the plant. Liquid kelp helps with both.