I tried mantra meditations, when I started my spiritual journey. But, by my opinion it is very demanding. Actual practice takes many years to first results. So, I tried another way, meditation about a name of a higher being like as its done by bhaktiyogis, see for example Ramakrishna and his vision of goddess Kali. Only meditation about a name, the best when you inhale (breath in? sorry ma bad English). And best with a particular wish.