Where do the soils tend to be heavy, well drained, compacted or sandy? Was the site an old landfill area? What is the slope aspect (north-facing, south-facing, etc.)? What are the micro-climates on the site?
Grading, planting, maintenance and invasive species control are all elements that require forethought, possible professional assistance and certainly flexibility.
You will have greater success. Scalping around the plants will give them a competition free zone in which to become established and makes maintenance easier. Knowing where they will be happiest (environmental preferences), reducing competition around them from other plants and giving them a little nutrient boost. If using a chemical fertilizer, make it a low N, balanced, 12-18 month release type. If using organics, try compost tea.
Most restoration failures are projects that have no maintenance component. Keep competition back. Grasses can overtop and suck the water away from their roots. Replace weed barriers. Pull fallen branches off of the little guys. It doesn’t take much, typically three times during the growing season is sufficient.