guard armies are basicly lots of low-point models, backed up by some heavy weapons teams and tanks.
i would get some units of Guardsmen, a Leman russ, 1 or 2 heavy weapons teams and either a basalisk or some sentinals. this will give you a strong backbone for your army, as well as a bit of variation.
THen it is up to you as to how you want your army to look. So read the codex and see what appeals to you and your playing style. I have seen tank heavy IG armies and I have seen pure foot troop armies with heavy weapons squads. It was the only time my 177 model foot slooging ork army had fewer models than my opponent. So it really is up to you and how you want your army.
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