Aeration is only needed when the soil is heavily compacted or completely dead. It opens holes in the soil and lets oxygen and other nutrients in to plant roots. The most convenient method is to hire a landscape contractor to poke holes or slice cuts all over the yard and then do the hand work in the beds yourself. Mechanical aerators are available in all shapes, sizes and features for rent or purchase. Just choose a tool or machine that fits your budget, because the cost ranges greatly. When you get oxygen into the ground, life in the soil and fertility increases. When the soil reaches a relatively healthy condition, the microbes and earthworms will do the aeration for you. Liquid biological products are better aeration long term.