It is often that people will ask you to solo over something that isn't the best tune for a bass solo. In those instances there is sometimes the option to take a walking bass solo. You already know the changes because you have been playing them over and over by the time someone asks you to solo. Walking changes up the sound but keeps the tune moving forward in a nice way. The other given is that people always want you to solo over fast tunes thinking that you will slap. This is fine I suppose but in truth I often prefer soloing on slower tunes that are more open sounding and give the bass a chance to revel it's distinctive warm voice. Waltzes can also be nice places for a bass solo though people often don't think of that on the stand. Try to work out a few tunes that you know you might be playing and when the tune starts tell the band leader that you'd like to take a break on this one. That way you prepared a bit on your own and won't be surprised when it's your turn to solo. You can get a lot more out of this type of experience than constantly being thrown in the water unexpectedly and have to fight your way out with a flailing slap solo.. And one more thing. We don't really need to play Grandfathers Clock anymore, be adventurous, find new tunes to become bass solo standards.