Budget [Excalibur] build, with a melee focus, of course.
[Steel Charge] for buffing melee,
Efficiency + Duration for [Exalted Blade],
Strength for higher damage output (it falls of somewhat quickly in star chart unfortunately, so make sure to mod your weapons well).
[Flow] for sustaining a higher energy pool, which means longer [Exalted Blade] usage or higher amount of ability spam (the main thing to love about Excal is how you can rip apart anything in early game with Exalted Blade, including low-level bosses).
[Fast Deflection] for survivability, since you don’t have any good way to heal your HP, you need to sustain your shields, and this mod excels at that. Just hope outta combat for a couple of seconds, and you’re good to go.

Advice for beginners: Try not to take a Heat Eximus’s fire wave ability head on, it deals heat tick damage which can rip apart any early game warframe. If you see it, just run (or slash dash) away first then kill it while its ability is on cooldown.