I listened to a pediatrician and tried introducing cereal at 4 months. That resulted in major constipation and gas so we decided to hold off until 6 months. In that time, I did more reading about introducing solids and decided to try baby-led weaning. It started out ok, but the gagging really stressed me out and twice I had to do back blows to dislodge a food that the BLW book said should be safe for 6 month olds.

After the second set of back-blows, my anxiety was going through the roof and my son was also starting to seem very anxious and stressed during meals, so I decided to stop listening to zealots on the internet and follow my gut about feeding my son. It did not strike me as safe or healthy to offer my son foods that I would use molars to grind down when he had 2 teeth at the time. What I ultimately did was to offer a puree and a finger food with each meal. I would spoon-feed the puree only if my son turned towards the spoon and opened his mouth eagerly, I always followed his cues and did not force or coax him to eat more of the puree than he wanted. The finger foods I offered with each meal were always diced small and things that were soft and not choking hazards. For example, I would offer soft-cooked peas, blueberries that were squished or cut in half, scrambled egg yolk broken into small pieces, sweet potato cooked soft and diced into pea-sized pieces, tender pieces of chicken or meat diced or minced finely, Cheerios, etc.

If I ever had another child, I would probably do the same, start at about 6 months if the child seems interested and physically ready (e.g. able to sit up with minimal support) and always watch baby's cues and never force/coax the child to eat more. I feel like avocado is a great first food as it is delicious, it requires minimal preparation as a puree (really I just stuffed it in a blender with some breastmilk, later on you just need to mash it or dice it up). I introduced foods one at a time for a few weeks to see if my son would have allergy problems, and I always isolated likely allergens (eggs) so I could see if that caused a problem, but by the time my son was about 8 months old I really only worried about likely allergens and would let him try any table foods that were soft and finely diced.

I like the site Wholesome Baby Food for guidance on good first foods and how to prepare purees.