The optimum salary for most small businesses is often to keep the salary below the level at which national insurance becomes payable.
E.g. fuel, telephone - expenses that are not tax deductible for a sole trader or partnership but are for a company.
Benefits that may arise from having a company (e.g. car and fuel benefit)
Companies under your control NOT including this one
Extra savings possible by not extracting dividends that put your income above the basic rate tax band.