I recommend checking out the Vigyana Bhairava Tantra. It's a centuries old text that is highly regarded within Kashmir Shaivism, but it by no means requires adherence to Shaivist dogmas to be employed. It gives you 112 different methods of meditation you can experiment with, individually or by combining them. They range from concentrating on sensual experiences, like the taste of food and drink, to mental exercises like imagining one's body as empty and void, to meditation on the chakras and flows of prana.