1- No chemicals are to be used, none! No fertiliser, no pesticides, no herbicides. The more fertiliser the more dynamic plants are, particularly the thugs like nettles... Killing some plant species changes the balance and kills the animals who breed on it, you end up with a dull lawn instead of a species rich meadow.
2- Be lasy: see what happens by itself, understand and find the easiest way of improving it. Aim at doing virtually nothing at all. In case of doubt, don't do anything.
3- Always remember that the wildlife is half of the beauty: don't destroy the habitat if you want the butterflies, dragonflies and swallows
4- Feel free to add non native plants as long as they don't overwhelm the overall effect. You can always take them out if unsuccessful. There are no right or wrong. This is not copying nature; it is gardening with nature. We aim to make it more diverse than it originally was. A cosmopolitan garden.
5- Cut what you don't like but always leave quite a bit in different parts of the land, there will always be some insect living on it. Like bramble bushes for shelter and food or nettle patches for butterflies.
6- Change the conditions: Sometimes the easiest way to control unruly thugs is to radically change the conditions. Reduce light with trees, reduce richness of the soil by removing the top soil, change the humidity level of the ground.