There is a general relationship between the strength of a bond and the relative atom size and electronegativity of the elements involved. Bonds between atoms of quite different sizes tend to be weak. An example would be C-O (350 kj/mol) and C-S (260 kj/mol) single bonds. Oxygen is directly above sulfur in the periodic table so O is smaller (and closer in size to C) and more electronegative (O = 3.5 vs S = 2.5). The C-S bond is weaker and easier to break. A C-N single bond (290 kj/mol) should be favoured over a C-Br bond (275 kj/mol), which contains a larger bromine. This will be important, for example in SN2 reactions, in which nitrogen nucleophiles can displace Br on alkyl bromide substrates.

In reactions involving double bonds, sigma bonds are generally stronger than pi bonds so addition to pi bonds to produce new single bonds is usually favoured. Many addition reactions are essentially irreversible at room temperature (e.g. hydroboration), partly because of the swapping of a weaker C=C pi bond (270 kj/mol) for (cumulatively) stronger C-H (413 kj/mol) and C-B (372 kj/mol) single bonds. Expect pi bonds to be reactive in many situations.

Bonds formed between atoms that each have at least one lone pair are always going to be weak. Bonds in peroxides (RO-OR) are easily broken (O-O single bond = 146 kj/mol), which correlates with electron repulsion between lone pairs on adjacent O atoms that are close in space. Likewise, the Br-Br bond (193 kj/mol) and Cl-Cl bond (239 kj/mol) will break easily, for example in the initiation step of a radical-based process.

See here for a general discussion of bond strengths.