As with most Lego promotions, you must spend a required amount of money to get the 'free' item. Many folks also use promotion stacking on http://shop.lego.com which is the process of spending just enough money to earn multiple promotional items.
After waiting too long to order products at shop.lego.com to obtain the popular 40252 Mini VW Beetle promotion (sold-out online), I visited my local Lego mall store. This store had current promotional sets available including 40252 and the 40265 LEGO Friends Tic Tac Toe set. The purchase requirements were to spend $50+ for the VW Beetle set and $20+ in Friends items for the Tic Tac Toe polybag. Both are popular items and make nice child Easter gifts (especially for my 2 children).
While paying, I was told my $62 ($21 of that for Friends items) worth of Lego products wasn't enough to cover both promotional items. The cashier told me their store were given strict rules to enforce around promotional items and I needed to pick one. I ended up going home with the 40252 Mini VW Beetle set.
After arriving home, I double-checked if Lego's web site still allowed promotion stacking. It did after added one $59.99 Friends set in my cart. Both Tic Tac Toe and City Helicopter (replacement for the sold-out VW) promotional items were in my cart.
I then read a 40252 Mini VW Beetle review where MeganL from brickset mentioned she was able to get both promotions by "doubling up" at a Lego store.
To further determine whether my experience was a mistake or an unannounced in-store change, I contacted Lego customer phone support today.
The nice representative informed me that other customers have called with the same question after being denied at their store.
At least one store manager told this same representative she was given rules to deny promotions stacking. Her customers could only receive both promotions if they spent $20+ on Friends items plus another $50+ on more Friends or another theme.
Please let us know how your local Lego store is currently handling promotion stacking and if it's different than past months.
Disclaimer: Not all U.S stores may follow the new rule regarding promotion stacking. Lego's online website, https://shop.lego.com/ automatically stack promotions in the shopping cart before order check-out. Additionally, some stores haven't allowed promotion stacking since their grand opening.