To meet the requirements of new 5G use cases, two methodologies have been proposed. The first considers additional processing on orthogonal frequency division multiplexing (OFDM), e.g. windowing, filtering, and precoding. The other aims at the design of new modulation schemes. Essentially, any block-based linear modulation, such as generalized frequency division multiplexing (GFDM), can be seen as precoded-OFDM, where the precoded data result from the frequency domain modulation. This representation has a significant benefit for the implementation of new waveforms. Namely, the available OFDM transceiver techniques can be reused, whereas the required signal features can be fulfilled by the configuration of the GFDM modem. In this paper, we propose flexible OFDM precoding based on the GFDM framework. As a particular case, we focus on orthogonal precoding to enhance the performance in fading channels. By means of closed-form expressions, we show that all the sybsymbols within the same GFDM subcarrier attain the same signal-to-interference-plus-noise ratio (SINR) in frequency selective channel. In special precoding cases, all symbols achieve equal SINR. This feature is important to enhance the performance without a need for power allocation.