Bank cheques promptly.  Make it easy to pay you through BACS by including bank account details on your invoices.  Can you set up standing orders or direct debits with regular customers? 

Accepting cash brings security problems.  You may need additional insurance both for keeping cash on the premises and to cover staff taking cash to the bank.

Debit card payments now outnumber payments by cheque.  Contact your bank to find out what is involved with accepting plastic cards.