It depends what's wrong with the soil, eg is it heavy and clayish, light and sandy, stony or what? Different plants suit different conditions Most soils can be greatly improved by adding well rotted compost or farmyard manure - or anything fibrous really - my mum even once buried a very old mattress (filled with wool, not the sort with springs in!) You can mulch with dead leaves over the winter, or even grass mowings at a pinch, it all helps.

So test your soil - pick up a handful and squeeze it - does it stick a bit, stick and go squishy or easily fall apart again? (Not the best time for this as everything is so soggy at the moment) Have you done anything to improve it? Once we know the answers it will be easier to recommend suitable plants. What is doing OK now and what died? And what does well in neighbours' gardens?

Agree totally with Stera. we need more info to help you…

Is the soil acid or alkaline? Most plants will grow in neutral soil but some plants prefer acid soil and won't do well in alkaline soil and vice versa. You can get a pH meter for little money or a soil testing kit.