Read the guitar tab carefully before you begin playing. This will make you familiar with the fingering, difficulty and tuning of the song. If the song seems too difficult for your personal level of ability, try another song until you feel comfortable and confident playing the solo.
For example, some of the easier solos for beginners include "One of These Days" (Pink Floyd), "Feel Good Inc." (Gorillaz) and "Lover" (Devendra Banhart). See the Resources section for links to all of these tabs.
Notice in particular the fingering of the tab. Bass solos are known for moving your fingers up and down the fret board with speed. You might be playing the first string, second fret one moment and then the fourth string, 12th fret the next. Do some standard hand and finger stretches before you play or practice your solo to keep your fingers flexible.
Pay close attention to the notation of the bass tab. For example, bass solos are likely to include at least one of the following: a slide, a hammer-on, a pull-off or a muted note. Missing important notations such as these can change your bass solo for the worse. If you are not sure what a tab notation means, see the How to Tune a Guitar link in the Resources section.
Invest in some good quality equipment. You will only write the best bass solo if you are confident with your gear. Bass solos require you to be comfortable with your guitar. If the bass is uncomfortable to play in any way, try adjusting the guitar strap until you feel more secure. Your guitar should be like an extension of your body.
Improve your finger movement and speed. Any solo--whether it is a bass or guitar solo--requires your fingering to be precise and fast so that your solo will sound professional, clear and melodic. Practice running scales to improve your bass fingering.
Learn some of the key bass solo skills, especially the slap and pop bass techniques. A slap technique involves literally slapping the bass string with your thumb to create a fat, bouncing sound. Alternatively, a pop requires the player to pull the string and release it back onto the fret board, thus creating a popping, pitched sound. Use both of these techniques together to create a complex, authentic and impressive bass solo.