Mars also lacks a significant magnetosphere to shield its atmosphere from ionising radiation - this allows hydrogen to be lost to space, while oxides accumulate at the surface.
Like Earth, its composition is mostly iron and oxygen. Significant inputs of hydrogen could increase the water volume, while also releasing lots of heat- this would likely be one of the main terraforming processes. However it would have to be an ongoing process as there's no easy way to synthesise a magnetosphere.
You could try wrapping it in coils - induced EMFs from orbiting though the sun's magnetic fields could mean the coils wouldn't need powering, and again they also generate heat via Joule's second law. Less extreme would be an array of independent coils dotted around the surface. But on Earth our field is mostly produced by our active geology, caused by convection currents of molten core material - some of which is due to residual heat from the formation and subsequent re-formation following the collision with Theia, with the rest due to ongoing decay of copious radioactives... Tidal heating from Lunar drag is also likely to be a factor. Inducing interior processes like this on Mars would be very challenging. Trying to kickstart it by fashioning an artificial moon (say from Kuiper belt material) would likely cause mass volcanism that would take epochs to settle down...
As for life, you need relative stability while still having viable energy gradients (so there still needs to be some kind of inorganic activity providing the grass roots). Geothermal energy from tidal forces could suffice in the absense of stellar radiation. And then you need a sufficiently complex chemistry - presumably diverse enough that it can become auto-catalysing - that is, given an ongoing source of input energy, the chemistry needs to be varied enough that reactions can catalyse new compounds that will themselves catalyse the formation of new compounds, ultimately culminating in the development of molecules forming the roles of proteins and enzymes. The most flexible chemical base for this is of course carbon, followed by silicon, then maybe arsenic / selenium.. I expect "life-like" autocatalysing systems are extremely common.
The big black swan event in the eventual evolution of sentience was the development of mitochondria - basically the "fuel cells" that cells needed to remain efficient while contributing to a multicellular network. The emergence of life so early in Earth's youth, and the unbroken ubiquity of unicellular life for the next 3 billion years, suggests that life is cheap and abundant, but multicellular life extremely rare, and sentience might only happen a few times per galactic lifespan...
