Swales and terraces.

While it's raining is obviously the best time to see if there are any areas of your garden that have run-off areas, which may result in erosion.
Depending how much space you have you can make some swales or terrace type arrangements to catch that water and send it sideways, so it can percolate into the soil better.
Best suited to large open spaces on slopes, the swale is a trench across the slope, with the soil from the trench placed on the low side to make a mound.
Plants are grown on the high parts or in between swales on the slope, to make maximum use of the gathered rain and organic material that gets washed down into the trenches.

On a much smaller scale, simple use of small berms or bowls around newly planted plants can aid immensely in gathering water to soak in around the root zone. When you give it water it all soaks straight down, rather than washing away.
Tree bags are often used for revegetation projects, where they are placed around young plants to collect water for the seedling. They catch extra rain, but also gather dew in the mornings, and help protect against evaporation in the immediate area. A tree bag with a small berm around the seedling or young plant gives it a much better chance of survival in a tough environment. Some lucky plants even get a pulped cardboard mulch mat to keep the weeds at bay. These too reduce evaporation.
It all depends on the scale and number of willing people there is to carry out the work.