The squash bug nymphs are back already and destroying(and infesting)
my lettuce and they have already killed the cucumber and squash
seedlings.

Well, so you know which plants the squash bugs like. Try going a year
without planting those plants. Or if that is too much, at least plant
them in a different place than the squash bugs were last year.

Be willing to do some hand-picking of insects (potato bugs respond
well to this, for example).

Try to get your soil fertile (compost, manure, whatever you have
available) which can leave your plants a bit less vulnerable.

Plant a wide variety of crops. Rotate their locations (never grow the
same annual in the same bed two years in a row). If a plant is
consistently getting attacked, try another species or another variety.

Experiment with plants which may repel some pests (e.g. marigold) or
attract beneficial insects.

My firsthand experience is that I haven't had a lot of insect issues
which are big enough to prevent me from getting a good crop. I'm not
really sure whether I'm just lucky, or whether these practices have
prevented problems.

Organic gardening (as I've learned it anyway) is a bit more than
just replacing your malathion and physan with neem and diatomaceous
earth. There isn't one simple solution, but a variety of techniques
based on different situations and trial and error.