One piece of advice is never going to be enough.
It's a multi-stranded thing - you can't do everything that needs doing though - you do what you can and get better at it. I'd say make sure you don't just work in your garden - make sure you enjoy it by sitting out to read or listen to the radio.
OK various things -
You can't expect your soil to enable everything to grow - you really have to look after your soil by putting organic matter into it so you need your own compost heap - ideally 2 bins or you can make one with wooden pallets - keep mixing it up with the fork and better to get some of the compost out of the bins and in to your garden instead of leaving it in the bin. I buy a ton of soil improver most years and get rotted manure from local stables - just turn up and take as many trugs away as you like - you are helping them. I put fine wood chip down and occasionally buy bags of manure if I'm planting things like roses - which I was never very keen on until I started buying them from David Austin.
Plant some young trees - they take years to grow - so best to get them in early in your gardening life if you are staying put I have put in 2 acers, 3 silver birches, 4 magnolias, a rowan, 2 amelachiers, a bay - probably some others too - all different to one another.
Get several water butts - plumb them in to the downspouts if you can - I have 4 x 220L - rainwater is so precious in the hot weather - you have to go out and water plants, shrubs and trees - it's actually something I quite like doing in the evening.
One big thing - choosing plants for your soil type and planting in the right location are important, improving your soil is too but the 3rd most important thing I've learned is that knowing when and how to prune is really important - don't neglect to look up advice for every plant you put in.
4th point - a tip I suppose - it to look around at other peoples gardens around where you live to see what grows well and looks good - you can always ask the homeowners what the plants are if you happen to see them around. If not - take a photo and use Google Lens on your phone to analyse your photo and give you some hints as to what the plant is - I've found it works very well if you take good close up photos.
5th point - nothing wrong with an untidy garden - it's impossible to keep on top of absolutely everything.
6th point - if plants aren't thriving - consider moving them or even culling them to make way for something that might do better. I've moved an acer after 7 years to a shadier spot and a camellia that has never flowered in 5 years - I think it's been too close to other trees that have left it a bit dry.
7th point - I tend to buy smaller plants and let them learn to live and grow in my soil - I want to buy some broom (Cytisus 'Boskoop Ruby' - I had one but it has not done well this year - it's been a brilliant plant but parts have died this year - so I've dug it out but want another) - I won't buy the biggest one I can - I find the smaller plants tend to fair better in the long run. I'm also after another buddleia - I have 2 already - the bumblebees and butterfly's love them - once again I'll buy something smallish and let it establish itself and I'll buy something different to what I already have.
There is always so much more to learn.
HTH