Start with the grass
Bring long grass down in stages. A first cut on a high setting, then lower over the next couple of cuts, stops the lawn being scalped and makes it easier to see what's underneath, like rocks, toys and hoses.
Then the beds and shrubs
Pull weeds from the garden beds, roots and all, and cut back shrubs and creepers from paths, windows and fences. Leave big trees, and anything near power lines, to a qualified arborist.
A layer of fresh mulch on the cleared beds keeps new weeds down and makes the garden look finished.
Get rid of the waste
An overgrown yard makes a lot of green waste, far more than the council bin will take. Book it to be taken away in one go rather than filling the bin for months. See rubbish removal.
Keep it from happening again
Once it's back under control, a regular mowing round and a hedge trim two or three times a year keep it there. See garden clean up and hedge & tree trimming.
Get it done
Get a fixed price in writing, usually the same day: garden clean up, rubbish removal or hedge & tree trimming.