Recording analogue synthesizers needs to take into account a number of challenges. First, because of all the cabling, it is very easy to get ground loops which can cause hum. Tuning stability can also be a problem, and so waiting for internal temperatures inside the synthesizers to stabilize after power-up, and then frequent tuning, may be required, even in a temperature-controlled environment.
Most analogue synthesizers have mono outputs and so need to be panned or fed into two sets of comb filters to provide positional information in a mix, and they may sometimes require gating to prevent noise from escaping into a mix. In addition, the wide usage of low-pass filters in subtractive synthesizers can result in a mix becoming bass heavy, and a little high-pass filtering can help to remove this.
To produce polyphonic sounds from monophonic analogue synthesizers, you need either several synthesizers or to record the same one several times (tuning!). This can have unexpected side effects: slightly different rates of glissando, portamento or LFO modulation can sound very impressive.
Analogue synthesizers also have either limited effects (chorus in string synths) or none at all. Adding external effects to a synthesizer can produce a number of effects: echoes set to almost the clock rate of a step sequencer will produce syncopated rhythms that almost repeat an interesting contrast to the exact and predictable timing produced by digital synthesizers or computers with tempo-synchronized effects.
Using just the pre-echoes and turning off the rest of the reverb, or vice versa, can be interesting too. Adding distortion to monosynths (polysynth chords tend to just produce noise) and playing guitarinfluenced melody lines can produce a very distinctive sound.
To be played in context, synthesizers should be arranged in stacks, with a synthesizer on top of a string machine, on top of an organ or electric piano. Two-handed playing on different keyboards was much more common than split keyboards, except for the lower-cost multi-keyboards which mixed strings synths a VCF-based brass effect with a monophonic bass. Having two separate sounds and no restriction about which hand plays high or low parts (or both simultaneously) can be an interesting challenge, and one that can undo the legacy of piano lessons.
Early analogue synthesizers do not have memories for the sounds, and so the performer needs either to have multiple synthesizers or needs to change the sounds during performance. Given the cost of analogue synthesizers at the time, performers learned to change the controls to create different sounds. This required practice and a good familiarity with the synthesizer's layout and controls. Commonly changed parameters for these 'fast edits' include the VCO waveforms, VCO2 detune, VCF cut-off frequency and resonance, attack time and decay time.
Because analogue synthesizers normally have live controls, parameters would often be changed during the performance, and so if any of the settings were not right, they would be changed with one hand whilst playing with the other. MIDI controller boxes and DJ controllers are the modern equivalent of this live parameter adjustment from the 1970s.
Memories were often very limited: the Yamaha CS-80 had four 'user' memories which were actually tiny control panels.
Analogue synthesizers abound in clichéd sounds (some might say nothing but), although fashion and retro are cyclical, and if this is seen as bad, then waiting awhile may reverse the situation. Clichéd sounds can be used to advantage by avoiding the other clichés contextual sounds of the time: syndrum sweeps, spring-line reverbs, classic electronic drum sounds and 16-step sequencer bass lines (or by deliberately using all of these).
Monosynth melody lines have some characteristic patterns of clusters of note playing followed by a held note being bent upwards or vibrato added (not unlike some guitar-solo clichés), and there are many examples on keyboard-oriented albums of the late 1970s and early 1980s that can be used as tutorials.