As newbies to anal play we had a couple of tapered silicone dildos that worked nicely to open up the sphincters (there are 2). Now that we are more experienced, my wife simply does the 1, 2, 3, 4, 5 drill. Starting with a single finger and progressing to all 5.

We've also found that by going down from 3 to 2 say, as part of the build-up is quite effective - and feels great. Although I cannot take her fist, by the time she gets her fingers and thumb into the act - I'm ready for any of the dildos that we have.

Since you've been fisted - this is probably child's play for you - but maybe others will find it useful.