Yes,
patience is the key. Just like anonymissimus said.
I often use the first 2-3 rounds just to rally my troops. Usually around the camera room. If there are single soldiers somewhere in the base, I hide them until I have some more in the vicinity.
These first 2-3 rounds I usually note (on a sheet of paper) how many aliens are present, and where they are.
Then I start to advance very slowly. Step by step from cover to cover. I found it useful to send teams of 2-3 solders. Some teams to attack the enemies front, others to fall to their flanks at the same time.
I have built my bases (not intentionally.. just had luck ^^) to have long corridors. These are guarded by my snipers. They are in cover, leaving it every round to take a look down the corridor and then pop back to cover.
The tactics I use depend on the enemies behavior. If the enemy advances (you can see it through the cameras) I try to trap them somehow: Hide and wait for a good moment to leave cover and wipe 'em out.
If they stay stationary...guarding their spot... then it's up to me to advance with a lot of caution.
I don't use smokes inside the base (besides of emergencies). There is enough cover to hide. But in general smokes help a lot!
But of course there can be some frustrating situations. Hovernets and especially Combat Hovernets are really 'pita'. Having lots of TU and enormous firepower they can easily cover a long distance and still killing 1-2 soldiers.
And sometimes I get surprises because I'm still not very familiar with the buildings inside the base. Some have basements through which the enemy can sneak behind my lines (happend once). This nearly got me a heart attack
All I can say is you have to give yourself a lot of time to defend the bases. If you're not sure whats in front of you just stay where you are until you know. If Hovernets are present, stay away until you know what they are up to and you have a good chance of taking them out. Patience and caution.