While you are waiting for the weather to warm up, there are a few things you can do to prepare your garden for summer.
Finish pruning any dead, diseased or rubbing branches; and do any thinning needed to open tree canopies to more sunlight. Remember to prune birch and maple until after they are in full leaf (July), since they ‘bleed’ from open wounds in the spring. Although the sap that runs out the tree will not harm the tree, it’s more for the aesthetics of the tree.
Wait to prune spring flowering shrubs until after they bloom, otherwise you will be pruning off this years flower buds (e.g. Lilac, Forsythia, white-flowered Spirea, Caragana, Mockorange, etc). Although, shrubs that flower in late summer should be pruned now, late winter/early spring, before leafs appear (e.g. pink-flowered Spirea, Cotoneaster, Barberries, Potentillas, Ninebarks, Hydrangeas, Willows, etc.).
Now is the time to cut back your upright grasses, prior to any new growth. If you wait too late into spring, you will end up cutting the tips of new growth off. Note: do not cut back mounding grasses such as Blue Oat Grass and Blue Fescue, only prune out the old flower stocks.
It is best to wait for your garden to dry out somewhat before working the soil, or even walking through it, to prevent soil compaction.
Other than that, there isn’t much to do except tune up your mowers and sharpen your pruners.