Mimicking other, non-keyboard instruments

In addition to the standard keyboard instruments listed above - which happen to fit well for a generic synthesizer-workstation-do-it-all instrument - you may be asked to create the sound of other, non-keyboard instruments. For example, a brass section or a violin section. Or an accordion. Maybe a harp or a marimba. In my opinion, this is risky, because it can sound cheap and awkward, if you hear a horn section or an accordion, but none are to be seen on the stage. But that's nevertheless done quite routinely by keyboard players. In order to come up with a credible marimba part, you have to know what and how is played on a marimba.

If you're tasked with mimicking a non-keyboard instrument like a harp, you do whatever it takes to do that on your keyboard. Left or right hand? What rhythm patterns? Whatever a harp usually does.

What are some common rhythmic patterns? What I'm practicing now is very basic and quite boring (usually just quarter notes for both hands). How can I make it more interesting?

Quarter notes are actually quite a lot of rhythmic hits already. Start by playing just on beat one of each bar, and with your right hand only. Record your playing over a song that doesn't have keyboards, and listen to it later on. Is your keyboard part making the song better or worse?

But I get the impression that experienced keyboardists often won't play like this in a real pop/rock band situation, especially if there is already a bassist.

You're on the right track here! But you need to look at all instruments, not just the bass. And consider that the drummer actually plays several instruments: the kick drum, the snare drum, the hi-hat, etc. The guitar is capable of stepping on all the toes and fingers of a keyboard player and vice versa. A lead singer is the most important single instrument. How does your playing relate to the lead vocals?

What are some common rhythmic patterns? What I'm practicing now is very basic and quite boring (usually just quarter notes for both hands). How can I make it more interesting?

Quarter notes are actually quite a lot of rhythmic hits already. Start by playing just on beat one of each bar, and with your right hand only. Record your playing over a song that doesn't have keyboards, and listen to it later on. Is your keyboard part making the song better or worse?

• (1) rhythmic comping. Like guitar strumming, but on a keyboard. This can be (a) two-handed left/right alternation ("stride"), (b) one-hand backbeat like in reggae, (c) chord arpeggios in a steady rhythm. You need to think about what the rhythm pattern is. If your group was a salsa band's rhythm section, which part do you play - conga, timbale, shaker, clave, cowbell? Do you double an existing rhythm part, or play complementary counter-rhythms?
• (2) background pad. You play slow pad sounds which create a harmonic background filling. Either full chords or even just single-note lines. A high legato strings sound that stays as close to some single pitch as possible in a voice-leading sort of way can glue together the whole sound of the group. In a chord progression C, F, Gsus4, G, C, your single-note legato line would play the notes C, C, C, B, C.
• (3) melodic fills. You play countermelodies and "fills". For example with a brass sound or a "heaven/fantasy bell".
• (4) melodic doubling. You double an existing melody and give it more power. Either in unison, or e.g. a third/sixth above or below.
• (5) special effects. Come up with a strange sound and add it sparingly somewhere in a song. It may catch the listener's ear and make the song memorable.
• (6) full piano accompaniment. All of the above at the same time. You play as if there were no other players in the band, and others adjust to your piano playing. This is typically done in slow ballads. It's also a potentially dangerous thing to do, if others don't agree with you taking the whole stage.
• (7) synth solos. Well, not everybody does this at all. You play like a guitar solo, but on a synth. Impress everyone and show off what you can do.

It depends on which musical element (of the listed 7 things) you're doing. If you're playing synth pads, you only need one hand or one finger. You don't have to use both hands. As a matter of fact, you don't have to play at all! One of the common mistakes that pianists do is when they try to play keyboards, they play too much all the time, "full piano accompaniment" all the way and they never shut up. Don't do that! Do one thing only. Play a tambourine if you absolutely must do something with your hands all the time.

• (1) rhythmic comping. Like guitar strumming, but on a keyboard. This can be (a) two-handed left/right alternation ("stride"), (b) one-hand backbeat like in reggae, (c) chord arpeggios in a steady rhythm, (d) any other rhythm. 3-2 clave? Bossa nova? You need to think about what the rhythm pattern of the whole group is. If your group was a salsa band's rhythm section, which part do you play - conga, timbale, shaker, clave, cowbell? Do you double an existing rhythm part, or play complementary counter-rhythms?
• (2) background pad. You play slow pad sounds which create a harmonic background filling. Either full chords or even just single-note lines. A high legato strings sound that stays as close to some single pitch as possible in a voice-leading sort of way can glue together the whole sound of the group. In a chord progression C, F, Gsus4, G, C, your single-note legato line would play the notes C, C, C, B, C.
• (3) melodic fills. You play countermelodies and "fills". For example with a brass sound or a "heaven/fantasy bell".
• (4) melodic doubling. You double an existing melody and give it more power. Either in unison, or e.g. a third/sixth above or below.
• (5) special effects. Come up with a strange sound and add it sparingly somewhere in a song. It may catch the listener's ear and make the song memorable.
• (6) full piano accompaniment. All of the above at the same time. You play as if there were no other players in the band, and others adjust to your piano playing. This is typically done in slow ballads. It's also a potentially dangerous thing to do, if others don't agree with you taking the whole stage.
• (7) synth solos. Well, not everybody does this at all. You play like a guitar solo, but on a synth. Impress everyone and show off what you can do.

It depends on which musical element (of the listed 7 things) you're doing. If you're playing synth pads, you only need one hand or one finger. You don't have to use both hands. As a matter of fact, you don't have to play at all! One of the common mistakes that pianists do is when they try to play keyboards, they play too much all the time, "full piano accompaniment" all the way and they never shut up. Don't do that! Do one thing only. Play a tambourine if you absolutely must do something with your hands all the time.

What are some common rhythmic patterns? What I'm practicing now is very basic and quite boring (usually just quarter notes for both hands). How can I make it more interesting?

There are no rhythmic patterns specifically for keyboards that you could always add to any song without thinking, and a rhythmic pattern's being "interesting" does not necessarily make it a good fit for a song. The whole band together creates one big rhythmic pattern, and your job is to understand the big picture and what your own playing does to it. Even if everyone plays something that is extremely "interesting" by itself, if they don't serve the same idea, putting them together will create chaos and rhythmic noise. You have to contend with being a small part in a big puzzle.

Quarter notes are actually quite a lot of rhythmic hits already. Start by playing just on beat one of each bar, and with your right hand only. Record your playing over a song that doesn't have keyboards, and listen to it later on. Is your keyboard part making the song better or worse?