In Bhagwad Gita, Lord Krishna had said that anybody who worships me with utmost devotion, I will be pleased by their worship. It doesn't matters what he or she was offering to me. Patram pushpam phalam toyam yo mada bhakta prayachhati.
Similarly Shiva was pleased very easily because he was also known as ashutosh. You can only offer water and belpatra on ...
There are several mantras for Shiva Parvati like; -
Om Umamaheshwarabhyam namah,
Om gauri shankaraya namah,
Om Parvati vallabhaya namah,
Om girija pataye namah,
Om Ambika pataye namah,
Om Uma pataye namah.